Browsing around facebook this morning I came across the Second Friends application, which allows you to verify you avatar name and attach it to your profile.
The system is quite simple: you need to go to the Eduserv Island and click a sign, to generate a key, which can then be fed into the registration page on Facebook. The sign automatically offers to open a webpage and navigate you to the right place to register once you have clicked the sign.
Currently although I have a few friends on Facebook, and several of them are on Second Life too, none of my friends are registered with Second Friends. There is also a mysterious box to be bought for $0 which updates your status in Second Life.