I'm currently holding out to upgrade my PC til after the first few series of DX10 compatible video cards come out.
Cause I'm buying FSX and it's designed aroung Vista/DX10 so I'll look to be getting Vista for that upgrade, but MS OS's are always expensive and I can see myself going "ouch" when a look at getting it
But by that time a few people from work will have had Vista for a while and I can query them on how it goes.