With any past MS OS you really needed to wait about 1 year after is release to get a fully functional OS.
(Warning: Microsoft propoganda in full effect. Please take with a can of salt.)
With Vista things should be different. THe O/S technically has been in the "release" phase for about the past 8 - 12 months. Microsoft is telling partners and developers the reason for the delay in deployment is that they are building a knowledge base up for the new product. It's no secret that when 2000 and XP were released you would call MS for a solution to a problem and they wouldn't have one for you. Vista *should* change that.
Now if you believe all of the above b/s then more power to you. It will be a very good o/s just like XP was a very good o/s however it's going to take some time to get it up to a satisfactory level of operation. Today's hardware is going to get it's ass handed to its self by vista. When xp came out everyone was pissed because 256mb of ram wasn't enough. Today we sport 1-2gb without hesitating.
Wait until 6 months after release. Then you should be able to make an educated decision. Or be like me, adopt early and use it as an excuse to upgrade.