The way I have always worked it, the one who asks the other one out does the treating. In my line of work, I get an awful lot of free tickets to shows and events, so I do an awful lot of the asking.
All of my friends (romantic or not) seem to be quite generous - I get asked out maybe five or six times a month. Usually I'm working, so I can't go all that often. Actually, generosity is one of the qualities I need to see in someone before I can think of them as a friend - and I really hope I live up to that standard as well.
Honestly - I'd say I maybe break even, but I just don't keep tabs.
Pangloss
Postscript: Sorry for the absence - I was in the wilderness with an orchestra. Honest.
-p