Google recently launched a new service called "Latitude" which lets you publish your location, and let your friends subscribe to it. You can think of it as Twitter with some pretty tight location integration -- you can update your status, and your friends can stalk you.
Click here to see a video about Google Latitude
I believe the most successful applications are ones that step over the line a bit, and make people invest in believing it's going to make things better rather than worse. A good example of that is when Facebook released their "news feed" in 2006, which at the time seemed like a huge privacy problem, but now is just a fact of life.
It's going to be interesting if this actually takes off -- my gut instinct is telling me that its going to be slow going, but my theory makes me think that something like this could be successful. Since Google isn't really thought of as a social platform yet, it will be a lot more challenging for Google than if a company like Facebook did the same thing.
Are you going to use the new service? If not, would you use it if it was offered by Facebook instead? Let's hear what you have to say in the Talk Back!