Use Quicksilver to look up words
We here at TUAW are in love with Quicksilver. If it were legal for a man to marry a piece of software I do believe that Quicksilver would be on the receiving end of my advances (and hopefully it won't have a copy of Textpander or that could get awkward).
Quicksilver can seem like magic to some, and it does have a very steep learning curve, so any tutorial that I come across which explains how to use this program to accomplish a task is of interest.
Tim explains to us how to use Quicksilver to find definitions in Tiger's Dictionary.app (another favorite application of mine, but I wouldn't want to marry it. We're just friends). If you don't have Quicksilver you should download it and give this tutorial a whirl, it'll hook you.