We all know the Dictionary pop-up built into Tiger is excellent. I use it throughout the day, whether to define a word while browsing the web, or to find a synonym in the Thesaurus while writing an email -- which brings me to the cause of this hint. Why did Apple make the keyboard shortcut for accessing the Dictionary (Control-Command-D) so similar to the keyboard shortcut for sending an email in Mail (Shift-Command-D)? After the second time I sent an unfinished (and unedited, i.e. potentially embarrassing) email, I had the idea that changing the keyboard shortcut might be a good idea.
Just go to the Keyboard & Mouse System Preferences panel, and click on the Keyboard Shortcuts tab. Scroll down until you see "Look up in Dictionary," and double-click the existing shortcut for that command. Change the shortcut to something you prefer; I happened to pick F7. Now when I need to look up a word, it's just a quick tap of the F7 key away.
There's an unexpected bonus to this change, too. Previously, if you wanted to look up multiple words with the pop-up panel, you'd press and hold Control and Command, then hit D, then move the mouse around (while still holding Control and Command). With this reassignment, there's no need to hold the key down, which makes looking up multiple words easy. F7 seems to toggle "look up mode' on, and then hit F7 again to toggle the Dictionary off when you're done.
[robg adds: I wouldn't normally run a 'redefine a keyboard shortcut' hint, as it's somewhat generic. But the change in behavior when looking up multiple words was worth noting. I thought that I'd still have to hold F7 down to remain in lookup mode, but nope, it's a toggle key now. This is a big timesaver -- I love being able to just pop into a lookup mode, and then back out again. Easier on the fingers, and much faster, too!]

