FriendLynx helps you find your Facebook friends on Twitter

Also,

Even if you just started with names, it would be possible to be slightly smarter than just looking for the individual names.

For each name you found, you could scan its immediate social network and see if that contained a match for any of the other names. Putting this together might pull up the whole social graph.

Add more networks and publicly available information and I'd expect a name-list could come close to uniquely identifying each name on the list.

Project anyone?

The frustrating thing about using an app like this, that lives in the cloud, is that I have to expose my Facebook profile to it to get its services. And who knows what kind of app it will become the future.

Essentially, I'd love to find Facebook friends that use Twitter but I never, ever use any Facebook apps, everything about them seems totally dodgy.