Over the last several months, I've come to the realization that I am a middle-click junkie, and I am convinced that if you knew the power of the middle click, you would be too.  Just start trying it - specifically in your favorite tabbed browser (Firefox and IE 7 come to mind.)  Middle-click any link to open it in a new tab.  Now middle-click most any document tab title in a variety of applications (Notepad++, tabbed browsers, RSS Bandit, Visual Studio 2005, etc).  Yep, a middle-click on the tab title closes it.  Cool, right? 



One more set of handy keystrokes: I'm sure you know about Alt + Tab, but do you know about Ctrl + Tab?  Ctrl + Tab is a way to switch tabs - in ALL tabbed interfaces (including dialogs, etc.)  You guessed it - Ctrl + Shift + Tab goes the other way.  Give 'er a try!