AOL leads the pack in instant messaging, with about 41.6 million users, followed by about 19 million using Yahoo Messenger and 14 million using MSN Messenger, according to ComScore Media Metrix.
One advantage to Google Talk could be its ability to connect with users of competing services. The service is based on the Jabber open-source standard, which allows consumers to connect with other messaging systems that work with Jabber, such as Apple Computer's iChat, GAIM, Adium, Trillian Pro and Psi.
I'll say this,don't bet against google