Windows 7...

...it's not that different from Vista internally, but it does indeed run loads better on every PC I've installed the RC on. Its 'backward driver compatibility with Vista' further states how similar the core OS components really are, doubt there was any more than a marketing reason for upping the kernel version all the way to 7...

I'd classify Vista being notorious in the similar fashion Windows Millennium was back in its time. I've personalty dodged Vista any way I could ever since the Beta came out, no wonder the "downgrades" to XP were so popular in the community. 

On the other hand Windows 7 RC's so far behaved like Vista was meant to be initially. There's no constant sluggishness about it and constant HDD I/O. I'd classify Windows 7 as being "the new XP". The new taskbar comes in very handy (seems as if they've pretty much copied the years old dock from MacOS X, same deal with wallpapers changing). 

• Changing resolution's much easier to access compared to Vista
• Resource Monitor's long time coming
• File copy/paste dialogs and functionality are still pathetic (lucky there's Total Commander to fill in the gap)
• System tray's been cleaned up in a workable fashion
• Automatic driver updates are more useful than ever
• ReadyBoots seems to actually work properly this time with an SD card
• Indexing seems not to bring the entire HDD down to it's knees, even with Vista's long overdue HDD I/O priorisation
• No telnet client by default just like in Vista, it's not the telnet client which is unsecure but the server. Telnet's extremely useful for troubleshooting network comms!
• Maximum Performance power setting has somehow got WiFi power savings enabled by default, instead of WiFi maximum performance
• Virtual Hard Disks is a plus which I've only read about so far
• Windows manager mouse gestures are handy, however primitive compared to Linux windows managers which are far more intelligent and functional (eg. proper auto-placement of new windows and ALT+mouse resizing, moving...)

Apple summed it all up quite concisely.