For someone who loves keyboard launchers like Quicksilver, I have to confess an embarrassing deficiency in my keyboard competency: I've never really learned to select text with the keyboard. So I thought the topic would make for a nice beginning of the year Mac 101.
The keyboard text selection commands on the Mac are basically standard. To select text you hold down the SHIFT key and then use the arrow keys or HOME, END, PAGEUP, and PAGEDOWN. The left/right arrow keys (plus SHIFT) will increase the selection one character in that direction, if you hold down the OPTION (???) key the left/right arrows will select an entire word in that direction, and if you hold down the ??? key the left/right arrows will select to the beginning or end of the line. The up/down arrow keys (plus SHIFT) will select a full line up or down; with the OPTION key held down the up/down arrows will select a paragraph. The HOME key (plus SHIFT) will select all the text to the beginning of the document and the END key (plus SHIFT) will select all the text to the end of the document. Finally, the PAGEUP and PAGEDOWN keys (plus SHIFT) will select a full "page" up or down.
Basically the upshot is this: hold down the SHIFT key while in a text field and it will shift to text selection. Also, if you use the keyboard shortcuts without the SHIFT key they will move the cursor without selecting text. If you play around with and internalize these commands I think you'll find that keyboard text selection is often faster than moving your hand to the mouse. These commands can be really handy if you're selecting text in very small boxes where you can't see much (e.g. long names in open and save dialog sheets). One proviso: these shortcuts should work in all Cocoa applications, but they may not all work in non-Cocoa ones.