[Ramble]

1. Faster - That's right, it IS faster, games may not be up to full speed yet but features like ReadyBoost/Boot (they are the same service, but fulfill different roles) and Aero glass will speed up computing quite a bit. The caching features available are top notch.

2. More stable - You may not have any problems with XP stability (and neither did I) but Vista is far more stable, with better kernel locking and some driver separation from the kernel. Also, Vista has some excellent logging capabilities.

3. Security - Apart from Windows Defender being built in (which can be turned off and I do) the firewall is also far better, memory is protected better and UAC is pretty darn good. Also, slightly connected with the firewall topic is the improved networking.

4. Instant Search - Absolutely fantastic, very fast and very flexible.

5. Improved default apps - Some great additions have been made recently, Windows Mail is actually pretty good (despite being very close to Outlook). The built in calendar is great, and useful. Depending on the SKU you get, Media Center and Photo Gallery are also included. Nice little programs there. Old things like minesweeper and notepad have a new lick of paint to them. Also, I may as well mention the Games Explorer, while not a major feature, once you use it you won't want to go back.

6. Other shell enhancements - While some people hate various changes, I for one love the fact that metadata is included right in Explorer. Breadcrumbs are also great.

7. Power and mobility - Things like tablet PC input software is now included in all SKUs so no more separate versions. Power management is better (sleep is an example of this).

8. SP1 - The first service pack (and therefore OS) of Vista to upgrade the kernel to server-level reliability and speed (literally).

I can't be bothered to search for more improvements (it really depends on you for what you think is an improvement).