in my opinion, the first question you have to ask yourself is "do you want a faster way to interact with your computer?" we tend to forget how arbitrary our interaction with a computer is. and we also lose sight of how habitual the use of it becomes. even still, "no" is a perfectly good answer. i know a lot of people who are happy with their ui just as it is.

to someone who uses a computer a couple times a week, quicksilver would probably prove annoying. but to be able to take those thousands of little habits we have, and make each one faster, or make it go away completely... that's the sizzle. all the "command space," "create triggers," "macros" and "verbs," all that is the steak. the how. the sizzle is getting your time back (albeit a second or two at a pop).

is it intuitive? nah. it's just as arbitrary as any other user interface. someone has to tell you how to do it, and you have to take that and apply it to your situation. (in design school, the mantra was "if it needs instructions, it doesn't work" - a lofty goal, but a little pie in the sky for computer interfaces. they are arbitrary by nature)

quicksilver is a graceful, lightning-fast iteration of the user interface. it's like the difference between "start, programs, accessories, calculator" and having a calculator shortcut on your desktop. it only saved you a couple seconds... but if you use it all the time, you'll probably prefer it. of course, if you're like me, you put the shortcut on the desktop and forget it's there, and go to "start, programs, access.... DOH!"

what's unique about quicksilver is, it has access to the inner workings of the operating system and all the major applications in it, giving you countless combinations of things you can do. that's what makes it hard to describe. it's easy to describe ical. it's harder to describe the finder.

at the end of the day, if you would like to try a new interface... a "meta-interface" if you will, give quicksilver a shot. i've been using it for years, and i am just tapping the surface. it's hard to break all those little habits, but i'm cracking away at them one at a time...