We have a good amount of our infrastructure running on the Hyper-V release candidate, which has worked very well for us to date, so I was happy to see when Hyper-V RTM'd yesterday. We have already upgraded our Windows 2008 Hyper-V hosts to RTM and things are going smoothly so far. The full details on upgrading can be found here, but the short version is that you need to install KB 950050 (x64 link, x86 link).