Essentially Windows 7 will be what Vista should have been in the first place. Vista has essentially been the "Beta" version of Windows 7, used as a trial to iron out all the issues of an operating system that was late, not finished, full of bugs and resource intensive. What can be seen of Windows 7 so far has been impressive.

If you are looking at upgrading your current machine and you are using Windows XP it may pay to wait. With no direct upgrade path from XP (or earlier operating systems) you essentially have two options, A: upgrade to Vista then upon its release - to Windows 7 or B: a fresh install when Windows 7 is released. At this stage a fresh install seems the better way to go, this way there are no remnants of XP (or Vista for that matter) to plague you in the future. The main disadvantage with this method of course is that you have to reinstall all of your applications again. Windows 7 should finally bridge the gap between the aesthetics and security from Vista and the stability from XP to provide a nice balance between performance and security.

As a last thought you could always use Linux which has provided these all along