Google has announced the beta of Google Talk. It has IM and voice capabilities, like Skype and AIM, basically.

The cool thing (or scary, if you’re the paranoid type) is the integration with Gmail - you don’t need to establish a separate account if you have a Gmail account. People who’ve added you as contacts show up in your list when you register, and you can choose to accept their I-wannabe-your-contact request.

I think a lot more people will sign up for Google Talk than for Skype, because of the familiarity of the Google brand and the huge Gmail user base. On the other hand, Skype will probably receive more usage as people become more aware of and interested in IM/voice apps and want to compare the two.