Not using CR (use Lightroom) but I've been running Vista for almost a year now. Originally, it was a bug-fest. I am not going to try to recount my frustrations.
HOWEVER - and I'm not a Vista defender and have no real interest in this (am running 5 other machines with XP still) - in the past few months the Vista machine has gotten very noticeably better. At this point, compared to the various XP machines, it runs everything that's running on the other machines equally well...neither better nor worse. Many programs and drivers that were originally incompatible have been fixed or released and I wouldn't make a buying decision at this point based on the OS unless you are aware of a specific problem that hasn't been resolved on a machine that's well-maintained.
FWIW, you also should bear in mind MS's limited support/sunset policy on non-current (I won't say obsolete) OSes. I tried to reload the OS on a 98 machine last year and found that MS had NOTHING available. I found all the old service pack CDs but it was luck that I had them (and could find them).