First thing after Installing vista will make anyone struggle for there device drivers in case of an OS upgrade on existing hardware, second thing one has pool in extra cash for upgrading memory, graphics card etc etc to get boost in performance, without it one will go dead with sick OS from Microsoft.
Third thing if one is running OpenGL applications then either application will cry :( or out of the box dead. Vista is real bad with OpenGL applications, same applies most non OpenGL applications which might be running smoother with earlier OS 2000-PRO or XP-PRO but refuse work at all on VISTA.
Last most important thing is for gamers, all the guys from gaming world will be really unhappy with their respective games performing when running them on VISTA compared to XP, I would suggest XP users not to upgrade to VISTA – because XP is best workstation OS ever created by MS from all perspective --stability, reliability with total dependability and well supported by all software vendors.
As Microsoft claims that its development team has been working around 5 long years on changing complete functional core architecture in VISTA when compared to earlier XP or 2K platform but finally what actually people got is an OS with no future, just another sick Microsoft strategy to mint money from innocent people, who doesn’t really know, care or aware what actually goes into their computers and importantly is it worth the cost.