There have been several startups doing the same sort of thing, all failing. I'm still not convinced people want this (Location aware social networking mobile thingy). It's a shame you can't get traffic figures so easily for mobile apps - without user/revenue numbers it's all speculation as to how successful or otherwise loopt is.
I don't use my cell for networking. I don't like that constant connectivity. But within that market, I would suggest that the Dodgeball team is a force to be reckoned with.
Perhaps I'm biased because Loopt is ugly as sin, and Foursquare is slightly better.
IPO seems like crazy talk to me.