I attend cons for several reasons (not necessarily in order):

1) To buy things: If it's a big con with a lot of out-of-town dealers this is usually my main reason to go, since my local establishments don't carry a whole lot. This is my main reason to attend ColdWars/Historicon/Origins/Gen Con.

2) To run lesser known games. If I have some favorite games that are little-known (or very new) that I'm really nuts about I'll run them at cons in order to get more exposure to the game. So you won't see me run Settlers but I'll run Airlines (Alan Moon) or Fantasy Rules! (miniatures).

3) To play games I've heard about that piqued my curiosity and I want to know more. I own several German games but there's a lot I haven't played. If the con had a lot of German games being run, or some of the newer miniatures rules being played, I'd probably go to see if the games were worth sinking money into. There would have to be several of these games being run to be worth the trip. Another reason to attend the big cons as there's more of a chance these games will be there.

4) To win a tournament - this doesn't drive me much anymore, but I suppose if I was "super-into" MTG or 18xx train games I might go to play 2-3 days of non- stop MTG or 18xx stuff and nothing else. I don't have the desire to concentrate heavily on a single game anymore so this option is very unlikely.

5) To support a local con. If local people are running a con I will usually run some games as a GM, (see (2) above) but odds are I won't play in anything. I'll be running Formula De and some airlines-type games at Council of 5 Nations in Schenectady, NY this October. I have noticed that a lot of con attendees in recent times seem to be quite the opposite of me. They tend to stick to games they know which is the usual stuff like MtG, Axis & Allies, Warhammer, Settlers, Battletech. If it doesn't fall into the "safe & known, plus widely available at the local shops" category, they'll look but won't touch.