20 Useful OS X Tips. I usually don't blog tip lists unless there's at least one that will probably change my life, and in this case, it's #9:

To select a block of text, click the start position, then Shift-click the end position. Significant;y, this doesn’t just work in editing applications like Word (where you might be already doing it anyway), but it also works with non-editable text, such as a webpage in Safari.