I've been doing "ballpark runs" all summer. Just got home from Wrigley, watching the Braves beat the Cubs for ballpark #13 this year. Wrigley is walking distance; for Comiskey I took the El; everything else I've flown to, but not always on UA. I'm intentionally leaving some parks for future years.

I think Priceline might be a better candidate than United, considering how you'll probably need hotel rooms and rental cars too. Also, dotcoms may be bigger suckers for this kind of thing, even given the current state of the economy.