Here's a proposed UI improvement for checking in and going private:
http://www.flickr.com/photos/factoryj...
Right now it's extremely problematic that this is a separate/two-stage process. There are at least two reasons for this:
1. when I check in somewhere, Brightkite broadcasts that immediately to my friends. If I want that location to be private, and click the slider, it would have been too late -- my location would already be revealed (yes, this has happened to me).
2. If I need to click the privacy toggle FIRST and THEN checkin, I'm confused, because I might not want the previous place where I was to be made private! Confusing!
The issue is that you've confused state with location, or separated them in an unnatural/uncomfortable way. Really when you change locations, you also want to change your privacy option -- or have the option to do so. When you save a bookmark to Ma.gnolia, you have the option to make the bookmark private, AS YOU ARE SAVING IT, not after you broadcast it to everyone!
Anyway, check out my proposed UI. It needs work, but should start the conversation.