Just back from Boston, which was, for a few days, the hub (Hub?) of professional historians doing their professional historian work. I think that the AHA is not a great conference for early-career junior scholars. My overwhelming sense was that the meeting was filled with graduate students and recent grads on the job market, and mid-career and senior scholars who are plugged in to the larger system (staffing interview committees, serving on editorial boards or steering committees, etc.). I don't know any historians who attend the AHA to find out where their field is heading (although I think that it is a place to find out where the profession is heading), but most of the modern language folks I know attend the MLA for exactly this reason.
There's also the weird professionalization stuff that goes on at the AHA. It feels a bit like Versailles--there's a lot of jockeying for position, and sizing people up, and sidelong glances at the name tags as people try to figure out if they've met you/interviewed you/read your work/should know you. I wish I'd seen this handy etiquette guide before I went.
I talked to a lot of editors about my book project, and it felt weird when an editor from one university press with whom I'd spoken saw me with an editor from another university press. We're not even dating yet, just getting to know one another, but it still felt awkward and slightly promiscuous. I did discover some cool new books, including this one, by a colleague of mine. I've just ordered it, and I can't wait until it arrives. Viva automata!!!