Maybe I'm missing something, but I can't find it.
Why isn't there a master calendar... in the spirit of evdb, but perhaps more RSS focused... I mean, why can't I see a calendar of every baseball team (minor and major leagues) all at the same time, all in my area? Let's say it's Friday afternoon in Kansas City and you're looking for live music... why isn't there one place that shows it all, in various levels of granularity? Or I want to play in a pick up game of frisbee or maybe soccer somewhere within ten miles of my house...
If each venue published their schedule as an RSS feed, it seems trivial to put this together. I know, I know, you're already working on it, but I wonder why no one has made the winner yet. This has 'natural monopoly' all over it.