I had an time amazing comic-con. If you ever get a chance to go, I highly recommend it (see:
Schwag Mountain). That being said: the lines are ridiculous, people lose their freaking minds for the slightest whiff of free shit and sometimes you feel like trapped in mash pit centered in California's unshaven, unwashed armpit. But I would wait and mash for a week for an opportunity to hang out around so much art, and culture and (most importantly) enthusiastic, awesome people.
I've been attending Con for the last three years, but this is the first convention where I worked. First and foremost I worked for
Mysterious Galaxy,
the local science fiction book store. They are awesome, and -as it turned out- awesomely important to the industry. Secondly, I worked Con for myself. More than anything, I wanted to practice talking to professionals and presenting myself neither as a fanboy nor a schmarry, grasping asshole desperate to promote myself.

Anyway, I think the first thing I learned is I should drop the word networking, as in 'I'm here to professionally network.' While there is nothing wrong the 'networking' (or even 'self promotion') per se, I feel like the term(s) has been sullied by the reek of desperation, the stink of 'think of yourself as a brand beyond any and everything!!!1!.' It's better to not label your interactions, better to just enjoy a conversation with cool people and try and make a conection afterwards (when appropriate). Moreover, when you say you're 'networking' it sounds like your making a bee-line for anyone you think might be important/useful. For me, I tried to talk to pretty much everyone and see what happened. I made some great friends at Con, friends that have nothing to do with publishing/writing. And for me, that's what 'networking' is really about.
Second thing I learned is that publishing reps are all traumatized by the time they've spent in the dank, dark slush mines. That yawning abyss of a billion unsolicited words -99% of which are crap- has left them fully aware of just how many terrible writers are out there; and how each and every terrible author is wholly oblivious to their own faults. So I think whenever you meet someone in publishing (especially if you've only been modestly published like myself) you need to put them at ease that no, you are not going to force your grubby, unedited manuscript upon them. My go to question for anyone in the industry (besides authors) was 'Hey -I'm sure you get this all the time- but I am an author who is querying, is there anything else I should be doing?' All of them responded 'Nope, you're doing exactly what you need to do, getting an agent' although one added 'and keep writing.' Good advice that, and something I intend to follow.
Third thing I learned is that kindness, competence and genuine enthusiasm goes a long way. And I don't think these are things you can fake, honestly. I got a chance to meet the editor of an anthology I just submitted to because I was talking up the first volume to a random attendee. I met the author of a YA series because (unbeknownst to me) he was in the Simon and Schuster booth as I was pitching his series to my wife as her next read. I honestly didn't know what I was doing, but serendipity is cool that way.
Fourth thing I learned is that word of mouth is king when it comes to getting people to read/buy books. However, an easier 'entrance point' to a story/world is like steroids for that word of mouth. I can't tell you how many people said 'My Friends told me to read Harry Dresden/Game of Thrones/Sookie Stackhouse and then I saw the TV show.' I think that, with the sheer hyperabundance of amazing work out there, giving readers a different media, low commitment opportunity to taste a story goes a long way in creating fans. Hence, I think authors should be constantly searching for ways to get their stories to sink tendrils into other media.
I got a lot of no's, but I think I got them in a good way. For example, I asked one of the reps/editors for a publishing house if I could go to their afterparty. She -with the sweet, utterly politic voice all the reps used- said that no, it was only for the Authors. Even though I knew this wasn't true (my boss for the week got invited) I said happily 'Oh, that's ok' and proceeded to have a couple of really nice conversations with her over the course of Con. I even asked how the party had gone, the next day and was rewarded with some juicy author gossip :). It never hurts to ask as long as you follow the Will Wheaton mantra of 'Don't be a Dick.'
I talked to a bunch of writers I admire, but not really about my own writing or my own journey getting published. I can only imagine that they get a little burnt out on strangers asking them to help them 'skip the line' and read a manuscript/introduce to an agent/subscribe to their crappy struggling word guy blog. I was happy to meet them, happy to share how much I liked their work. Because of my employ, I even got to have slightly longer conversations than the other fans even if it meant I had to talk while packing/unpacking boxes of their books.
I didn't give out a ton of business cards but that's ok. I think you just have to play the business card thing by ear. Personally, I only give them out if someone asks for one or If I honestly believe that they would want to contact me (based on some kind of rapport). As a con attendee three years running, I wholly understand how many flyers/promos/cards get handed out only to briefly incontinent the recipient before being trashed. Whenever appropriate, I wrote down names (I'm trying to get better at names) and continued my Comic-Con tradition of asking for sketches from the nonartists I hung out with (some of these separate they paragraphs). This helps me remember the people I talked to and -hopefully- will help them remember me too. In all things, I tried to be the kind of guy that I would want to hang out with.
One thing I haven't quite mastered is name dropping. Generally, I don't like it and I don't do it. At the same time, there is a way to do it right which demonstrates enthusiasm instead of an assholeriffic 'let me tell you about all the awesome people I know and how important I am by extension.'
The other thing I realized (even if I intuitively understood this before) is that being the kind of person that I would want to hang out with means asking questions instead of talking. My go to question for most people is 'What are you passionate about?' (I think it's a good, truer substitute for the the blandly mercenary 'what do you do?' and defiantely results in more interesting answers.) My go to question for authors in a reading setting is 'What question would you like to be asked but almost never are asked? or to put it another way, is there some aspect of your writing or literature that is important but people don't talk/ask enough about?' If I don't wanna go all meta, I'll try 'Are there any films that have been influential in your story telling?' (This is because authors always get asked what their literary influences are.) Basically, asking better questions -while being genuinely interested in the answers- is the best way I know to make a good impression.
The exchanging and remembering of names is incredibly simple and incredibly powerful. I'm trying to do it more often.
I guess that every writer (even this particular struggling word guy) dreams of the Cinderella sweep i.e. someone will 'see the spark in me' and offer to read/exalt my manuscript and from there all my dreams will come true. But in everything, I'm trying to exchange my fantasy of superstardom for a reality of work. Dreams come true, but since I don't have any kind of Godmother (fairy or otherwise) my dreams will come true brick by brick. As such, Comic-Con didn't change my life.
But I really and truly believe that I did some really cool work on my foundations. More than anything, Con was my succesful proof of concept that A) I can present myself as a professional B) I can talk to anybody thanks to my bit of charisma and bunch of practice and C) I really am the kind of guy that I would want to hang out with. Awesome. Now, its time to get back to querying agents and writing.
(I have a lot more sketches. If I hear about an interest via comments, I will post them.)