I've used Spaces right from the get go. I have been using some sort of multiple windows app for years. We have it at work with Unix/Linux, so I had to have it for at home on my various Macs.

As far as Expose goes, I use it a bit, but with 6 Spaces going, I don't need to use it too much.

I can't live without Spaces any more. I was a Linux user and had many virtual desktops in X. Switched to Mac and found it insufferable having to continually hide windows. Have been thrilled with spaces. I have one for IM, one for Mail and iCal, one for Firefox, one for Echofon, one for Emacs and Skim, and three more that get used for other apps when they're open. I can quickly jump to wherever an app is that I need without worrying about window positioning. I love it.

Expose, on the other hand, gets a great big *yawn* from me. I think it's because I always have an extra space where I can see the desktop if I need it, like mentioned above.