Tripit, which I mentioned in an earlier post about Planjam, is a do-it-all travel service that helps people organize their travel plans (flight numbers, car rental info, accommodations, etc.) in one central location that can be updated and accessed on the go. Today they're launching a new feature called "closeness" alerts.
Much like Dopplr, which we peeked at last month, the whole idea behind the alerts is to let you know when your buddies (Tripit calls them "colleagues") will be in town or traveling in or around the same place at the same time. The only things existing Tripit users need to do to get in on the alerts are a) have at least five other people as friends and b) make and share their travel plans either publicly, or by inviting their friends as viewers.
So how do the new closeness alerts affect privacy? What if you don't want other people to see that you're going on a trip? The good news is that the closeness alerts are setup the same way as any other trip on Tripit, meaning that if your trip is marked as private, the only other Tripit members who will be able to see it are those you invite to participate.
There is certainly a lot of potential for these services, especially if you've got a large social graph and wouldn't mind unexpectedly seeing your friends while traveling. It certainly beats a flight out just to see them, and assuming everyone uses the service, you might have a reasonable rate of success.