I learned a ton from the few panels I attended. I mainly looked for ways to fill in holes rather than to go to panels where I already knew a lot about the subject. Here are some highlights:
Victorian and pre-Victorian war stuff: I had no idea that you could keep a firearm loaded pretty well indefinitely if you prepared for weather. Some antique weapons still sitting in attics could theoretically fire just fine--so be careful whenever you pick up something firearm-like no matter how ancient, dusty, rusted, dysfunctional, etc. it might appear. I know, duh, but it bears repeating. Your great-great-great-grandfather's flintlock might be loaded and go off. Seriously. Plus, cannonballs traveled really, really far. They just bounced on and on and on for thousands of meters.
Seriously cool. I wrote down some good sources for those hard-to-find non-technical details that describe, for example, that black powder firearms emit a gorgeous, pure white smoke (the lecturer told us it's the purest white he's ever seen.)
Panel about consistency when writing in a series, shared world, etc.: The main good idea I got from this is to write notes and an outline after you finish a chapter in a book or a short story in a world that you may intend to write in again someday. Character details that are revealed (age, that she loves bourbon, etc.) plus a general list of events is all you need. One writer on the panel had to hire someone to read her books and take extensive notes for her to go off of because after several years she needed to start writing in the series again and had forgotten most of those telling details writers keep in their heads with varying degrees of success. Reading those books would have taken too much time out of her writing schedule and would have put her behind on several deadlines.
I'm going to start doing that from now on. Much easier and cheaper than hiring someone ten years from now to read Masks and take notes on it so that I don't mess up someone's mother's age and get hate mail from fans about it. (Wouldn't it be grand to get fan mail and to work with multiple deadlines on projects because I'm such a busy writer? I know, I know, be careful what you wish for ....)
I watched master artists sketching a life model (who was somewhat clothed for propriety's sake as it was in a public area) for quite some time. It made me itch to do art again, which is good because I also studied cover design at the convention, first at the art show and then again at a cover design panel and yet again at a 'what's coming out this year' panel for Orbit. (I missed the one for Tor, darn it!) My brain is now brimming with ideas--the perfect time to start rough design ideas for various book covers before those ideas vanish into mist.
I also talked shop with a Canadian publisher. I hope to send some stuff their way soon.
There's lots more to tell, but I ought to actually, you know, write. Today.
Right now ....