(Sorry for the hiatus, etc)
If you're using a Mac, QuickSilver becomes an invaluable add on very, very quickly. If you're not using, it stop reading and install it now.
Really, I'll wait.
Now that you have QS installed, here's a way to do really quick dictionary lookups:
Open QS preferences
Go to plugins
Add the Services Menu Module.
Note: Do *not* add the dictionary module - that will not work in 10.5.
Once this is done, you can open a normal QS window using your hotkey (mine is Apple-Space)
Hit "." to start typing free text.
Hit "Tab" to go the secondary window containing a list of actions.
Start typing "Lookup in Dictionary.app". Usually, I have to type "Loo" before QS figures it out.
Much better than going to dictionary.com or dict.org or even doing "define: foo" in Google.