What is Placeme? I've included a video, more than 30 minutes long, that is worth watching. I REALLY REALLY REALLY think you should watch it. It's an interview conducted by Robert Scoble with the creator of Placeme, Sam Liang, a former Googler.
What Placeme does is use the sensors on your mobile device to track you. Scary yeah? But there is a lot of potentially good use from the data that the app can collect and help the user. It can use the ambient light, accelerator, Bluetooth, GPS, and other services on the phone to keep a log of your daily routine. It will eventually know how you get to work, when you get to work, where you go next (like a supermarket, bar, gym).
In the video, the creator gave an example of how Placeme was able to track where he walked through Walmart on Black Friday.
Scary? Definitely but I can see a lot of potentially good uses for this. There is a big debate raging no on Scoble's Google+ page. I suggest you check out the video and maybe even the app and decide for yourself if this is for you.