The screenshot above (no longer available, sadly--Larry) perfectly illustrates what I dislike about Foursquare. Somewhere along the way, the idea developed that we not only need to broadcast our every thought (à la Twitter), but also tell the world where we are at every moment of the day, regardless of whether the people to whom we're broadcasting want to hear it or not.
Personally, I find the idea of telling the world my location constantly a little creepy. I figure there's no reason to make life easier for psychos and stalkers, but that's just me. Unfortunately, Foursquare fills up my Twitter stream with cutesy messages that someone I follow on Twitter is now the "mayor" of something. For some reason, the "cute" aspect makes it particularly disagreeable. When I was more active on Jaiku, it was somewhat interesting being able to see a person's location, but the appeal wore off quickly. Making it an annoying, gushing statement with an exclamation! point on the end (and that I have no choice about seeing) doesn't make it any better. There are better ways it could be done; Foursquare's chief competitor, Gowalla, makes it a simple statement (like this) which is much less hyperactive, and consequently less irritating.
I've thought about unfollowing anyone on Twitter who insists on filling up their stream with this dreck, but the chief offender among those whom I follow is someone from whom I get useful information on a fairly regular basis, and I'd hate to lose that. What I really need is some kind of tool that would let me filter out the automated Foursquare spam and focus on the informative posts. If anyone wants to write a program like that, I'll gladly volunteer to do your beta testing.