I've been training in BJJ for a few weeks. A lot of people on here seem to post comments like, "Oh, well, I trained with some [whatever] guys and they couldn't hold a candle to my irimi-nage" or "After an hour of wrestling practice I defeated a judo shihan!" but unfortunately I have not been able to so easily transfer my knowledge. On the other hand I've already learned a lot of valuable information on escaping from bad positions. I haven't asked, "So, what do you do if you're attacked by TWO guys?" yet but I'm sure they'll have a really interesting answer.
A large emphasis is placed on sport/competition. I'm not sure how well I'll do with all this because I think I may lack the requisite aggressiveness. Struggling and squirming to put someone in a chokehold seems oddly undignified. In the meantime I only attend the "Fundamentals" class, though, and have learned a lot of great information about takedowns and positions.