InPrivate Browsing is Internet Explorer's answer to Chrome's Incognito and Firefox's Private Browsing. In essence, it gives you a very quick way to surf the Internet without leaving traces of activity on your computer.
The problem with Firefox and Chrome, though, is that there's no one-click way to open a private browsing window. You have to fumble with some menus or hit a keyboard shortcut, then type in a full website address (or you could wade through our guide on how to force your browser to start in private mode). With Internet Explorer 9, however, you can pin an InPrivate Browsing tab to your taskbar! Simply open an InPrivate Browsing session by hitting Ctrl+Shift+P, navigate to the site that you want quick access to, then drag the tab to your taskbar. Every time you click the icon it will automatically open the site InPrivate Browsing mode; easy!
Of course, this doesn't mitigate the fact that you have a highly-visible icon on your screen that links to something you're probably trying to keep away from prying eyes. Still, for shared computers where you don't want to intermingle Google search histories or similar, it's an excellent solution.
Update: as commenter Dan Larson says, if you right click any pinned site you have the option to "Start InPrivate Browsing." All of the major browsers have this feature in Windows 7 (and Vista?), incidentally.
For more IE9 tips, see our tips index, or read our complete IE9 guide.