Initial reports on this SP were scary so I pounded the crap out of it last weekend. Honestly, I didn't run anything under Vista because I wanted to test the core stability of the bit and I had no Vista machine handy anyway.
My conclusion is that this service pack is fine to run with. The fixes the dev team made to issues far exceed my expectations insofar as some of these issues have been around for a long time.
Good job to the devs at MS!