I'm guessing if you hover your cursor over a contacts name an image will appear,the other party (contact)
has to of uploaded an image,their basically over grown avatars.(i rarely use the web mail part of gmail,so don't quote me on this i use pop)
Just a guess,but i'm betting this will bleed into the features of google talk as well.
On a side note Google Pack dropped trillian from the pack,or maybe trillian dropped google...either way
their no longer in bed together.
If your using Opera,chances are it's not working cause google services and Opera don't get along very well.