In addition to what sq3r said in his yearly update, Windows 7 has some pretty nice new features on the window management side of things.
Aero Shake is kind of neat. Basically, it's like a "minimize all but this window" feature. Click the title bar and wiggle the mouse a bit to trigger it. Not sure how often I'll actually wind up using it, but we'll see.
The way Microsoft revamped the way that windows move is awesome. Windows that are maximized will automatically restore if you pull the title bar down. This makes moving a maximized window from one monitor to the next incredibly fast and intuitive. Being able to snap the window to one side of the desktop is very nice (it was even touched upon in one of Microsoft's commercials for Windows 7) and is something that I'll probably use quite often. The only "problem" with it is that it doesn't let you snap the window to the gap between the two monitors. No biggie; Win+Left and Win+Right will take care of that. It's better than accidentally snapping the window when you're just trying to drag something from one display to the next, at any rate.
The ability to launch applications on the taskbar using simple keyboard shortcuts is something that I've been longing for since the QuickLaunch bar was introduced (you know, in WINDOWS 95). Just tap Win+number to activate the object at that spot.
The search engine is much faster and more responsive than the one in Vista. Even when searching unindexed locations it was able to pop up some results almost instantly. The start menu search is lightning fast. It will generally give you some sort of result before you can even finish typing the word in (typing in "command", for "Command Prompt", gives me a result by the time I'm half-way done typing the first word).
UAC is far less intrusive without sacrificing security. While I am still keeping it off on my home system for various reasons, I've been running it on my work system for a few weeks now and haven't seen a reason to disable it. Only a select few system changes will trigger a UAC popup, making it far less annoying and chatty than UAC and any sudo-based solution I've seen.
It's a shame Firefox is so behind the curve when it comes to the new taskbar. IE is such a dream to use due to some of the new taskbar features that Windows 7 has had in place for MONTHS (they were in the first publicly-released beta, after all) that Firefox seriously seems clunky in comparison. Here's hoping they start supporting the new features in the next couple of versions.
I haven't messed with HomeGroups, so I'm not going to comment on that. It's a very cool concept, though. Workgroups are not a particularly intuitive way of putting any sort of network together, be it a home network or otherwise. From what I've seen, HomeGroups look like a simple domain setup, making it far easier to successfully connect to the other systems in the house (something that workgroups certainly DO NOT allow for, since it's merely an organizational method). Having a central password is far better for your average user's sanity than requiring logon passwords and the like on every machine (or modifying group policy settings).
Aero Peek is wonderful. It makes finding the right window incredibly easy. The thumbnails in Vista were nice, but having access to both makes it hard to make mistakes.
Progress bars can now be shown on the new taskbar, which is nothing short of awesome. Again, a feature that Firefox desperately needs to support.
The layout of the control panel and display personalization screens are a serious improvement over Vista. Vista made desktop personalization far more logical than XP (since XP follows the Windows 95 "put a bunch of unrelated crap into one screen" policy to a T), but Windows 7 goes the extra mile by both keeping things sensible and making them more intuitive. Rather than breaking everything up into separate screens like in Vista, Windows 7 merges the screens where appropriate, lumping most major aspects of user personalization (including desktop wallpapers, screen savers, desktop icons, mouse pointers, and the user's Welcome screen picture) into one screen and pushing the screen resolution into a different one. Quite nice.
The Action Center is a major improvement over the Ye Olde Security Center in XP and Vista. Rather than making it an all on or all off component, Windows 7 now lets you deactivate specific warnings. If you don't want it bugging you about disabling automatic updates but still want to know if your virus definitions are outdated, you can do it.
The Network and Sharing Center is a bit less daunting than it is in Vista. I'm still not particularly happy with the way that the interface is laid out, but at least Windows 7 puts some of the more advanced settings (such as disabling password protected file sharing in workgroup networks) a bit further out of reach of casual users, instead pushing the more intuitive features such as HomeGroup.
The system tray has changed quite a bit. Rather than having to go into that annoying "customize notifications" screen every time you want to hide an icon, Windows 7 lets you merely drag the icon off the task bar to hide it, and drag it back on to put it back in. You can also rearrange the system tray icons. If you want your volume control to be on the far left instead of the far right, just drag it over there.
As far as hardware support goes, Windows 7 has picked up every single piece of hardware in both my system and my dad's. Between my system and his, only his (old) TV tuner was unsupported. Basically, if Vista supports it, Windows 7 will.
So yes, it's definitely a nice OS. I'm very happy with it so far.
Edit: I forgot to mention this: Windows 7 is capable of installing video card drivers without requiring a restart. Freaking beautiful.
