Probably going to be a lot of talk about this over the next few days. Google has just released a first beta of Google Talk - ther own IM / VoIP client. Just giving it a try now, but it will be interesting to see how this competes with Skype, AIM et al. It uses XMPP so is actually a fairly open client (See the developer pages). They are also talking about supporting SIP which would be great. Also seems to have good integration with gmail. One to watch definately, I think the boys in Redmond may be moving more into this space as well.
UPDATE: Skype have announced a limited opening of their client base. Looks like the weight of Google is already having an impact. It's amazing how big the Google brand is. Considering this frst release of Google Talk isn't actually that good compared with what is in the market currently, the move is getting loads of press today. I heard reports in the (very short) news on BBC Radio 1 - even a mention in the New Scientist website. This may actually be quite good for Skype as it is getting mentioned against the Google Talk product - which means more people are getting to hear the name.