Back in June I asked about face recognition in photos using Linux.
An update: The new version 3.5 of Google's Picasa (Windows only at present, but see below) has face recognition and not a bad implementation of it either.
Now, given that Picasa on Linux is basically the Windows version bundled with a tested version of Wine, I thought I'd try the Windows version on my Ubuntu 9.10 desktop, and it installed just fine and works perfectly as far as I can tell - I spent some hours yesterday tagging some faces and watching as it went off and found other photos with the same people in them. I'm particularly impressed that having tagged by 4-yr-old niece it recognised her in her baby photos! It's a bit hit-and-miss (as you'd expect) but I'm impressed over all.
Obviously Picasa is beer-free not speech-free, the significance of which will vary from user to user.