Merlin Mann is really up in arms about Loopt's SMS invite system, and rightfully so. I think I may have accidentally done the same thing without realizing it. The app has some potential, but the setup process on it doesn't make it clear what it is doing. And Justine is saying that same thing on her blog:

There’s a good chance that if you installed this application you’ve made the same mistake that most people made. While searching for friends who were on the service, apparently a text message was sent out to a large portion of my contact list, along with my phone number and my exact location (you know, since that’s the point of the application). Granted, you would think that if you have someone’s phone number, they’d have yours as well…

I think I may have spammed everyone on my list with a text message from Loopt... Sorry about that. That app is about to get uninstalled.