Was playing with GoogleTalk earlier today. Very impressive entry in the IM space, but Google has a knack of springing quality products in different markets. It integrates nicely with GMail and has excellent voice capabilities. I would daresay it would take the place of Skype should it offer POTS integration in the future. In the meantime, I’ll be using 3 IM clients …
Oh, and it also integrates with other IM clients to offer Mac and Linux capabilities via the Jabber/XMPP protocol
(Comparison with Skype here)