GMail Inbox shows previews of Google user avatars when moving over the name with the mouse cursor:

http://www.flickr.com/photos/4563214/488171549/

My girlfriend sees this as well, and has for a long time. I don't :(

Also discussed here:
http://blogoscoped.com/archive/2006-05-12-n78.html

Since... a long long time
Even on Zorgloob we have a screenshot of what you said, from MAY 2006
http://www.zorgloob.com/2006/05/google-talk-son-et-lumire-dans-gmail.asp
http://mail.google.com/mail/help/images/photos-inbox-small.gif

It´s not new 4 me too.

Ciao qui in Italia c'è questa possibilità già dal 2006
Hi here in Italy we have this feature from 2006!