Typically, you'll see a history list of the most recent open files -- or Web sites, in the case of Internet Explorer -- as well as options to pin the application icon to the task bar (if you haven't already pinned it there) or unpin the application from the taskbar (if you've already pinned it there).
You can also unpin the three default task-bar icons -- Internet Explorer, Windows Explorer and Windows Media Player -- in this way.
Jump lists also make their appearance on the Start menu, in the Most Recently Used application list. A small arrow appears to the right of any application with an associated jump list. Click the arrow to see the list, then make your choice from the list.
There has also been a minor change to the Windows Shut Down button. Click an arrow to the button's right, and you get a list of shutdown options, including switching to a different user, logging off, restarting, locking the desktop, or putting your machine into sleep or hibernation mode.
Aero Peek
The other major change to the interface in this beta is the addition of Aero Peek, a nifty little enhancement to the Aero interface introduced in Vista that lets you "peek" behind any open window to your desktop. It's far more fully featured than the Show Desktop icon that lived on the Quick Launch bar in previous versions of Windows.
Aero Peek lives as a small, rectangular area just to the right of the clock at the right edge of the task bar. When you have windows open and you mouse over the Aero Peek rectangle, all of your open windows disappear, and you see through to your desktop. But you don't see just the desktop -- you also see the outlines where each of your open windows would be.
So, for example, if you have three open windows -- one near the top of the desktop, one to the left side, and one to the right -- you would see the outlines of each of those screens. If you prefer just to see the desktop itself, with no outlines, click the Aero Peek rectangle instead of hovering your mouse over it.
Aero Peek also works in concert with the task bar. As I mentioned previously, when you hover your mouse over an application with open windows, you'll see thumbnails of the open windows, and you can preview them by hovering over any thumbnail. That's Aero Peek at work. If you turn off Aero Peek, you won't be able to see the thumbnails -- you'll only see them as a stacked list. To turn Aero Peek on and off, right-click the Aero Peek rectangle, and either check or uncheck the box next to Preview desktop.
I did experience some problems with Aero Peek and the task bar thumbnails (which are turned on when you turn on Aero Peek). They worked only intermittently, then inexplicably stopped working entirely. I fixed the problem using one of Windows' built-in troubleshooters, but I don't know what caused the issue. I haven't heard reports of this happening to other people, so it's possible that the issue was specific to my test machine.