Under the hood, Windows 7 is a lot like Vista. Indeed, most of what gets us hot and not-so-bothered about is what's on top: When it comes to look and feel, the new UI is the biggest step forward since Windows 95.
The taskbar is our favorite new UI element of Windows 7. It's the biggest change from Windows past, and in our view, the best. But it might result in some confusion at first because it groups applications that are open and those that aren't into one big party—the theory is that it shouldn't matter if it's already running or not if you wanna open it. That might kinda remind you of OS X's Dock, but it works a bit differently and definitely still operates on the Windows paradigm. Combined with Aero Peek, which makes every window on the desktop transparent except the one you're highlighting at the moment, you can find any window nearly instantly, no matter how many windows your desktop is buried under.
Here's how it works: When you hold your cursor the icon of an open program in the taskbar (it'll have a hint of gloss it, while unopened apps are dull and non-glassy), a live preview thumbnail will pop up for every window it has open, and in applications coded for it, like Internet Explorer, a thumbnail of every open tab, too. When you hover over a thumbnail, it brings that window to the front, and makes everything else transparent, so you know it's the one you're looking for (or not). [More Taskbar details and images and why Windows 7 Taskbar beats Mac OS X's Dock]