Microsoft just announced the release of the Service Pack 1 release candidate for Windows 7 and W2008 R2. This will be the only RC release before the eventual RTM release. You can download it now. The download page still talks about the beta release. I guess that’ll get updated pretty quickly?
I haven’t seen any details on additional changes since the beta. I know that MS demonstrated an additional Hyper-V feature at TechEd NA 2010 that was not in the beta. This allowed Hyper-V admins to use PowerShell to configure virtual switches to filter out traffic from VMs if they used a non-assigned IP address – useful where you don’t trust the delegated admins of those VMs who are logged into them with admin rights (and could change the IPs to try do a spoof attack).