Ubuntu 9.10 is now out and despite some negative comments, that I suspect are more to do with the beta release than the final release, there is a strong message that this is serious competitor to Windows 7.
I have installed on my laptop and upgraded the desktop and both are working without problems.
If you have not yet tried Linux or Ubuntu I recommend you give it a go. For Windows users there is an easy install, non-destructive, under Windows, that will give you a dual boot system with an easy un-install option. here’s the link: http://wubi-installer.org/ .
I have successfully tried an install/uninstall on a Vista PC.