I haven't been to conventions with that, I don't think.
It's tricky because the word "convention" is really vague. In Manhattan, it means "pub crawl" (see: Santacon), for example. The events I'm particularly talking about are events run explicitly by people in Science Fiction Fandom as a non-profit gathering, typically with little media content, wherein people socializing in some way is the most important aspect. That is to say, not like "Creation Con", which is a for-profit event wherein you pretty much just buy stuff and get some famous person to write their name on a photograph (I never understood this).
Fannish conventions are basically a bunch of fen (that's the plural they use for "fan", because they really, really like puns) who get together in large numbers and just try to find different ways of having fun. Arisia in Boston, for instance, had the following items which are: extremely common to all of this category of convention:
- (getting this out of the way) The usual vendor room, but almost entirely filled with local merchants, which is one way for the poorer attendees to be able to afford to continue going to these events
- A free food room called a "con suite", where anybody can socialize at any time while enjoying generally snacky foods but occasionally real food
- An even better free food room for people who participate in (not just attend) the convention
- Panels discussing unusual subcultures among geeks (in this case, these discussions are often heavy with either topics on disabilities or on alternative relationship/sex lifestyles)
- structured dances; unstructured techno-ish dances (I think I even heard a few wubs this time around)
- hoop jams
- parties from around ~8pm to ~1-2am advertising other, similar conventions
- an area set aside for youngins to hang out without being creeped on
- a panel to explain how to probably flirt without being creepy
- a stargazing night with local astronomers
- a usually gigantic room set aside for gaming (sometimes just tabletop, sometimes also e-gaming)
- a big costume contest on a stage rather erroneously referred to as a Masquerade.
- a room that plays anime round the clock
- a room for Filking round the clock (this is a musical art which often, but not always, involves putting new lyrics to familiar tunes, but it can also involve original music that is particularly geeky)
- readings by local authors
- discussions about why Steampunk is so damned popular all of a sudden
- combat demos (with swords, or just martial arts, that sort of thing)
- masses of people getting sick the day after because somebody was too inconsiderate to stay home when they got the plague
- Belly dancers
- Also a ton of panels on the usual stuff, like hard science or books or tv shows or movies or costuming or anime or gaming or whatevs
Less common but more seen the closer you get to nerd college towns like Boston:
- parties from ~11pm to ~3-4am with insane amounts of UV lighting and [free] booze (in this case, often with dry ice making everything all smokey)
- generally some semi-official excuse to go into the hotel pool and hot tub (Arisia and both have a Pi-Con have a "Panel in the Pool", while Lunacon has an afternoon pool party with inflatables and suchlike)
- shadowcast performances (like Rocky Horror) of various films and TV episodes
- themed morning yoga (this year they apparently did yoga to Dubstep)
- fire shows (like fire poi, flaming hoops, firebreathing, that sort of thing)
- blood drives
- "play" parties ← not the Nintendo kind of play
- burlesque performers
These things give me maximum enjoyment for relatively minimal expense (not counting the hotel room, Arisia cost me $30 in five day admission and $7 to get there and back from Long Island).
Oh, neato, I could have just linked to this:
http://fanlore.org/wiki/Convention
Apparently "fancon" is the more or less official designation.
...holy crap, there's a convention specifically made for Starsky and Hutch slash fans. My mind is blown. :O