I went to a presentation on Windows 7 at TechEd, and the guy was running the latest build with all the task-bar-y goodness working. He went into a fair bit of detail about what it means for application developers.
They've merged the task bar, quick launch bar and custom toolbars together; running applications get a single icon (if they're on the taskbar already as shortcuts, they just get a visual indication that they're now running. Mousing over the icon for a running program gives you little preview thumbnails of all windows for that app (and all tabs in the case of IE8 - the application developer can define what's shown in the thumbnails).
The thumbnails can also have buttons on them, so for example, Media Player has your basic play/stop/fwd/back buttons. From the thumbnail, you can view a full-size preview of the window, or actually go to the window, if you really want to. The task bar icon can also have an overlay (MSN style indicators, for exampled), and a progress indicator. It's all quite nifty, although I'm not sure what mouse-phobic alt-tabbers will make of it, and it will no doubt piss of Peter Boughton for reasons that are completely different to everyone else's reasons for being pissed off.
There's also a right-click context menu for quick launch applications - it lets you see your recent file list or whatever (if it's that's kind of app) or open the app in certain ways (if it's that kind of app). For example - Word will show you your recent files, WinIPConfig7 would give you options to release and renew IP addresses, purge your DNS cache and that kind of thing.
The way the system tray works is being changed round, so that only things that the user chooses to have in it will be displayed in it.
Under the covers, they claim to have done a load of optimising, and have apparently made a load of efficiency improvements over Vista; the example the guy gave was DVD playback - you get an extra hour of hotel-room pornfapping out of your laptop battery with Windows 7. (He maybe didn't describe it exactly like that).
Also in Windows 7: Notepad Multitouch. It's awesome.
EDITED: 16 Nov 2008 22:16 by WINGNUTKJ