I installed the Windows 7 RC on my 2 year old gaming desktop. Noted: I skipped Vista on my home machines. These are my observations of 7.
1.) The system boots faster with identical applications loaded
2.) The interface is much snappier in day to day operations - the layout of menus, shortcuts, drives, and peripherals is more intuitive. *Can't give enough praise for the recent files used under each program (big time saver).
3.) Programs load quicker than XP and use of programs feels snappier.
4.) The Task Bar is what it always should have been. The new changes are extremely useful in day to day usage. I especially like the preview box of open windows in groups while pinned.
5.) Windows Explorer is light years ahead of XP. File management is so much easier now.
6.) USB support feels better. I'm getting higher reads/writes off existing usb keys/hard disk drives.
7.) The interface is nicer looking - I feel like I'm using a modern computer system. I really like the auto size when dragging windows to the side of the screen or top.
8.) No crashing or lockups as of yet. The RC has been rock solid (I wish I had been able to test the beta, people say it was even quicker).
Microsoft sold me on Windows 7. I purchased two copies of the upgrade to home premium for $49 each. I don't know why people say it's outrageous for the OS. I'm not sure you're using the same Windows 7 I am, but it's worth every penny MS is asking.
Noted: I'm an avid Ubuntu user as well.