I have just recently started using Windows Vista, the latest OS from Microsoft.  Although it is prettier than the aging XP it has little to offer the casual user.  Requiring nearly 500megs of RAM to run Vista be sure your system can handle it before adopting the new OS.  Here is a link to the Windows Upgrade Advisor.  You should probably pad the results a little for maximum benefit.   Keep in mind if you are running Norton Internet Security that it is a memory hog as well.  I recently switched to Trend Micro's PC-cillin Internet Security and find it much easier to use and more functional.

Beware of hardware driver issues when upgrading to Vista.  Many hardware devices I have (most of which were just purchased in the past year or two) do not currently have compatible drivers for Vista.  Even some of Microsoft's own products such as my MS Natural Multimedia Keyboard no longer function properly.

 In my opinion you can wait to upgrade.  This OS is supposedly going to be the fastest adopted OS in history with nearly 26% of users upgrading to Vista within the first 12 months.  However, with all the hardware driver issues and general lack of documentation on fixing issues among various 3rd party vendors I expect a much lower adoption as word spreads.