The Windows SharePoint Services SDK for v3 is now live. They also have an updated Developer Center that just went live too. Check it out, especially if you are interested in developing on the upcoming releases of Office Live, this will be a great place for you to start learning. One of the biggest changes for our next release is that we are moving Office Live from v2 to v3 of WSS.
We won't be supporting *everything* from the WSS SDK, but I'd say a majority of things you could do in WSS you could also do on the upcoming release of Office Live. There may even be a few additional goodies that we provide that WSS does not.
The Office Live SDK (mentioned previously in this blog) will have topics covering what we do and don't support.
Just to be clear, we're not talking about giving developers rights to install code on the Office Live servers. So don't expect to being able to install new web parts. You'll be able to integrate with our existing business applications and use any webparts that we provide. But you won't, for example, be able to write a web part that executes custom code on our servers.