I saw a friend using it a little while ago (week or so ago) and thought it must be a new feature, so I signed into Gmail and nothing! He was like, heh?! so later on I read through the new literature about it (that you linked to) and found out that it only worked if you had it set to US English...and I have (or should I say, HAD) mine set to UK English, so I simply switched them over and I got a nice little message saying something about the new features of googletalk - viola!

The moral of the story is, always change you language settings and see what happens!