I have worked in software developent for large projects, and believe me Vista was a large project.
When a large software project starts someone sets a date a couple of years in the future when they say it will be finished. This date is mostly guesswork as nobody really knows how long it will take.
But then there are delays, and then more delays, and then senior management start to get annoyed, and one of the senior managers will say "it has to be out by January".
So everybody works towards this January date. It will not be finished by then, but it has to ship no matter what.
That is what happened with Vista.
It has taken about five years and Microsoft bosses started to get annoyed.
So Microsoft said it would ship in January, but it was not finished in January. No matter, it has to ship anyway.
So what we have is an unfinished product.
I am sure there are hundreds, maybe thousands, of bugs and problems still in it.
I would wait for Service Pack 1, maybe Service Pack2, before going to Vista.
I remember someone saying to me once
"Software is never ready, it just ships every now and again"