Coming to Mac OS X from a Linux/UNIX background, the concept of multiple virtual desktops was quite familiar to me. So much so that I was a bit disappointed that Tiger (well, Panther initially) did not provide such a function. I managed to emulate it to some extent with Virtue Desktops in Tiger, and eagerly anticipated the advent of Spaces in Leopard.
Exposé, however, is a very clever concept. I use it all the time and have done so since the beginning. Combined with Spaces, it's absolutely brilliant for managing your workspace. I have space 1 dedicated to email and chat programs, space 3 dedicated to web browsers, space 4 dedicated to audio editing and iTunes, and space 2 to image editing and word processing. All spaces get Finder windows as needed for whatever a particular app might need (dragging and dropping documents, etc.)
I mostly use the keyboard to switch between the spaces, having remapped the switching key combo to be Command-arrow rather than ctrl-arrow because on my Macbook internal keyboard the command key is located adjacent to the arrow keys for one handed space switching. The ctrl key is located too far from the arrow keys if I'm not using an external keyboard. There is a control key adjacent to the arrow keys on my external keyboard (an old-school Apple bluetooth wireless) but I like to have one-handed operation of space switching with the keyboard even when I'm out and about with just the built-in keyboard.