I'm no expert on Google by any means, but I doubt they are going to be releasing an OS--that is, not in the traditional sense. For months there were rumors of Google releasing a mobile phone and/or a mobile OS. When the truth finally came out, Google was in fact heading up a coalition of 30-some companies to create a new, open source mobile OS called Android (more info
.) Google is apparently quite happy to help make a free mobile OS because it will just give them more platforms to plug in the services they already make money off of (search, email, maps, docs, etc.) If they develop or help develop a desktop OS, I bet it would be in a similar vein, though that's just a guess and I haven't actually heard anything specific about a desktop OS from them.