what does it REALLY offer?
Sure, its pretty. but pretty doesnt pay the bills.
Ok, the pulldowns in in the location bar of explorer are an improvement.. but im sure it'll be available in some form for free soon for XP.
Its slow on modern hardware
About the ONLY thing motivating anyone to upgrade is the new security structure (least privledged user or whatever its called), which most people actually find annoying anyway.
Bottom line? I don't forsee a lot of adoption. XP was miles ahead of 9x. 95 was miles ahead of 3.1. Vista is not really much of an actual productivity improvement for most users, so businesses and normal people wont bother with it for a long, long time. (unless forced)