One of the utilities programs that veteran Mac users swear by is Quicksilver which at first glance appears to be a keyboard-based application launcher.
It turns out that QuickSilver can be used for a great deal more than application launching, but a lot of the productivity that you can gain from it isn't at all obvious.
One of the best tools I've found to understand Quicksilver are two video podcasts from the MacBreak series. The first and longest one is MacBreak Episode 12: Quicksilver, which is available on iTunes, but is also available on Google Video (not YouTube):
In this episode you get to see how Merlin Mann selects something on his Mac by typing its name using Quicksilver, and then selects a command to perform on it. You can think of the the first action (a search) done in Quicksilver as the subject of a sentence, while the section action (selection of a command) is the verb.
By stringing subject and verb together, you are able to do things like use Quicksilver to find someone in your address book, and begin the composition of an email. I illustrate this below:
This technique is really productive when you are using Spaces and you aren't currently in the same space as Mail.app is. Think of how many separate steps there are in composing an email by hand under that scenario.This technique is just something I learned yesterday. It absolutely makes installing Quicksilver worth it to me. I think you will see many other potential timesaving techniques in MacBreak Episode 12 and a shorter companion video podcast, MacBreak Episode 17: Quicksilver Tips.