Summertop: I would most definitely call it a downgrade rather than an upgrade. All you get at the moment are some additional restrictions and obscure "security advantages" which are so annoying that everybody will ignore them/ turn them off after a short while. This article ("20 Things you won't like about Windows Vista" may be a good start, although I wouldn't agree on some of his statements, especially on his "OS-Ranking". It definitely shows some disadvantages from the user's viewpoint.

Anyway: I have not heard of any reason to switch to Vista except its improved look&feel (which is IMHO inferior to the look&feel of other modern OSes like MacOS or up-to-date Linux distributions) so far.