Google Talk is just another IM client, including voice. The difference between Google Talk and other IM clients appears to be that you are required to have a Gmail account to use this one.
So the Beta that this is doesn't really offer any revolutionary new stuff, but I'm sure the Google Team has a few aces up their sleeves. If they don't, why did they even bother creating Google Talk in the first place?
(hint: right now,
GAIM gives you much more versatility and agility)