Facebook introduced "mention tagging" for apps using Open Graph today, meaning you'll now be able to @ mention your Facebook friends while using Foursquare, Foodspotting, and SoundCloud the same way you do on Facebook itself. Mention tagging is different from "action tagging," which Facebook has offered for a while and is only meant for when you and a friend are doing something together, such as checking into the same restaurant.
This feature gives users more control over how they want to share information when they use an app. And it gives developers more options in the kinds of sharing that they provide. By letting users decide when they want to bring the Facebook connection into their third-party app experience, Facebook may be making good on the idea of "frictionless" sharing it heralded when it first introduced Open Graph at f8 last September.