I think i'm going to wait until the official release also. I wonder when sp1 will be release for vista
according to this link, aint SP1 for vista out? http://technet.microsoft.com/en-us/windowsvista/bb738089.aspx
Its an RC, so its not the final release of SP1. I'm 99% sure that service pack 3 is still in RC. The final release will be sometime this half of 2008. The RC wasn't even released THAT long ago anyways.
you can install the xp sp3 rc now, and when the final one comes out, uninstall rc and install the final.