Coupon seller Groupon has acquired social ratings service Ditto.me. Ditto launched a little over a year ago as a check-ins app for the iPhone, which would let you see what your friends are planning to do. Foursquare-like in its check-ins feature, it was built to favor a tad more interaction--with it, your friends would know where they might run into you before you got there. Also, the app would draw from your list of contacts to serve as a recommendations service for restaurants or movies. With Groupon's buy, Ditto's days are numbered. The company's Windows and iPhone apps are scheduled to be deactivated on April 30th.