After spending about 2 weeks evaluating Quicksilver, Launchbar and Butler, I've taken the latter two off my system and am going to use Quicksilver for the time being. If you don't know what a launcher is - it lets you launch applications, open folder, open urls etc. by typing a few keystrokes rather than having to mouse around finding stuff. In some ways they work like Spotlight, except that they don't search inside files, and they allow fuzzy searches that use just a few letters in order - so (for example) Safari can be invoked by typing 'sf'. Now that example leads to a couple of other observations - firstly, the shortcuts don't have to be standardised - up until now I've always launched Safari using 'saf'. The second comment is that the program learns from your responses. So the first time I used 'sf', Quicksilver suggested “Sara Foster” - a contact from my address book. But when I didn't select that in a few fractions of a second (adjustable) a list of other possibilities popped up and i down arrowed till I found Safari. But the second time I used the abbreviation 'sf', Quicksilver automatically brought up Safari as the default, so a quick Return popped me over into my browser. And if I do want to see Sara Foster's details, all is not lost - invoking Quicksilver (a user selectable keystroke - I use Control-Space) and typing 'sfo' and Return immediately presents me with Sara's details in Address Book.
Quicksilver not only launches (or opens) things - it can also do many different actions on relevant objects too. So for example, after watching a funny video, a few keystrokes will automatically attach the file to an email message to a friend (selected with 2 or 3 letters of their name) and (depending which action has been trained to be my default), send it straight off with a previously created template message (“Thought you might like this...”), or it can open up my email program with the address and attachment already loaded, so I can write a longer message.
Different modules allow Quicksilver to interact with many programs, so I use it to browse, start, stop, and skip iTunes selections; it's possible to use it to directly manipulate graphics files (eg. scale a photo and convert to gif).
There's heaps more to Quicksilver as the following tutorials (and here) or reviews (or this comparative one) show. For my money Butler did just too many things and so was a bit complex to grab hold of - Quicksilver has many complex possibilities but works at a basic and easily understood level straight 'out of the box'. Launchbar seemed to have a similar feature set but three things turned me to QS instead: (1) a simple search for a folder I have called “Presentations” worked as expected in QS whereas LB gave me a great long list of presentation related things (subfolders, bookmarks, documentation) in which my folder was not listed; (2) QS looks cooler (I'm a Mac user after all!); and (3) QS is $19.95 cheaper, costing just $0.00.
If you're a Mac user, check it out - I think it's going to change the way I work for the better and save me from carpal tunnel syndrome as well.