Beta version is here:
http://www.microsoft.com/windows/windows-7/default.aspxI played around with it for about a half hour and I'm pretty impressed so far. It kind of surprised me by picking up my dual monitor setup immediately after installation. I didn't have to touch a thing!
I haven't tried running OpenGL applications in a window yet...I'll have to remember to do that. That is probably the biggest disadvantage that Vista has over XP (at least when Aero is enabled...as long as you're not running DWM it performs just as well).
The new start bar is...interesting. It's definitely Microsoft's take on the OS X dock, but I find Microsoft's version a lot easier to chew on simply because it isn't centered (in OS X, you can't reliably select programs by "feel", you always have to look because the bar constantly expands and contracts), but I'm still not too crazy about fully icon-driven interfaces. I haven't really played around with it enough to really know whether I really like it or not, though. One thing that is very nice about this is that, as a result of this change, the icon size has increased. Rather than having tiny 16x16 icons, the task bar now has what appears to be 32x32 icons.
Some of the UI oddities in Vista have been addressed, with many dialog boxes being cleaned up.
UAC is now more adjustable. By default, it won't prompt the user for changes to system settings. I still doubt it'll get people to stop BAWWWing over it since the problem that plagued UAC is third-party software, but that, plus the fact that UAC has been out for two years at this point (i.e. if you haven't modified your badly written application to work with it, shame on you), things should be a bit smoother.
The classic Start menu (i.e. the Windows 2000 one) has finally been removed. The only start menu available is a tweaked version of the Windows Vista one (the only change I noticed at a glance was that the shut down button gives a full text description of its default action). Thank goodness. Forcing people to use the new start menu might finally get them to realize how incredibly backwards the old one is from a user interface perspective.
The Security Center was replaced by the Action Center. Same basic layout, but the name is a bit more all-encompassing. It keeps the alerts separate from the list of things checked, making it much easier to see what it's fussing about. As always, the alerts can be disabled.
The system tray and the notification area appear to have been combined again (in Vista, some system controls, such as the network connection icon and volume control, were separated from the system tray). As always, it gives you the option of hiding unused system tray icons. That's pretty useful, but now it's even better. Windows 7 lets you selectively disable balloon notifications for each system tray icon (disclaimer: I didn't get to play with this yet). Each balloon pop-up also has a little wrench icon that appears next to the close button that allows you to change the notification and icon appearance settings.
The Windows Sidebar doesn't appear to be in Windows 7 in its normal state. Instead, Windows 7 moves the Sidebar gadgets right to the desktop, ala
DesktopX. Since one of the advantages of the Sidebar, as it appears in Vista, is that you can always access your widgets regardless of what's running, Microsoft went ahead and provided a little button to the right of the taskbar that allows you to very quickly page back to the desktop. I'm not sure if this works like Win+D (i.e. working great unless you make the mistake of popping open a new window) or if it's properly implemented feature, ala OS X's Expos