Nouns and Verbs...

To use Quicksilver you bring up the input window using Command-Space and then start typing the name of the thing you want to work with. It can be anything on your hard drive; it can be a document, a folder, an app, a contact, a playlist. You name it.

Here I've typed "SMU" and it suggested Smultron. Launch is what it's going to do when I press Enter.

But there's more...

If the thing is a file like a jpeg, instead of an app, then the panel that says, "Launch" would say, "Open" instead; but as well as Open I now have over 20 other things I can do with that file: I could now type OW and it would offer Open With... then I'd type TOY and it would suggest ToyViewer...

There are zillions of actions that can be performed, depending on the file-type, and people are coming up with new plugins for Quicksilver all the time. I've been using it for months and I've only scratched the surface of its capabilities.

The look of the app can be changed very easily...

...And the way it presents information is very sexy as well. Below are examples of a Large Text Bezel, and an iTunes Track Playing Notification.

Why "Nouns and Verbs..." as a heading? Because it seems to me that the basic philosophy behind Quicksilver is that you enter a noun (the name of an object), and then enter the verb (what you want to do with that object). It's a lot more than that, but even that's plenty for now...