I would always be willing to pay on a date. I don't expect the guy to pay, but if he is asking me to go somewhere and do something, then it'd be nice if he did, but like gypsygirl said, I'd probably try to make it up by buying us ice cream later or something.
I think I'd want to casually discuss it beforehand, hopefully, before we ordered, just because when the waitress comes around and asks "Is this together or separate?" I wouldn't want that awkward moment of me looking at him and making it seem like it's all on him to decide, but then not wanting to offend if I say "separate...?", so either discussing it before ("Hey, I've got dinner covered") or if he's super quick when the waitress asks and saves us that moment of awkwardness, ha.
I can think of a few things I want to do for dates where we'd compete to see who paid. My bread-on-the-geese one, for example, or a water gun game during the summer or something, where if you lose you pay. Just to have more fun ways to decide and add a little competitiveness but...I'm competitive and he better not "let" me win.