Among those that won't become switchers, Microsoft's own worst enemy is itself, as
it needs to prove that Vista is a worthwhile upgrade to XP when XP is already so refined. For many users in the consumer space, Vista is simply a version of Windows where (to borrow a quote from Field of Dreams) "If you build it, they will come." These people will get Vista on their new computers and they'll like
it because
it is good, but having never had the chance to decide if they didn't want it.
For everyone else who does get a choice, more often than not we believe the choice will be Vista. As we've stated before it's not perfect, but it's quite good. There are some very good reasons not to use
it in some cases (system requirements, compatibility, and OpenGL performance), but for those machines that the above do not apply to, there are numerous useful features in Vista that warrant an upgrade if you find that you're the kind of person that will use them. Vista's SuperFetch and Search technology are both reasons enough to migrate from XP, as they easily improve productivity and performance.

Vista is a worthy upgrade and an even better choice as an operating system for a new computer. At the same time there's still ample room to grow; hopefully we'll have even fewer complaints once Service Pack 1 is released later this year. Hopefully Microsoft will spend some time improving features as opposed to simply
bug fixing, though, as right now some of the design decisions still need work.
Source:
Techzine - Externe Review: Windows Vista Performance Guide @ AnandTech - ICT Nieuws / Community site