I'm not sure where I stand on this, however, I'd like to provide one data point, one that I expect many HNers share. I'm primarily a web developer, though I do frequently work on Android projects or random hacking on some python projects ( sage anyone? ). For web development, I find spaces essential. I have several api docs open at any given time, eclipse for android stuff, Aquamacs ( emacs in cocoa ), potentially an Android emulator, a preview image from our designer, several browser tabs for email, roadmap, and backlog tasks and a team chat window.

I, too, thought that most people wouldn't really care much for spaces, however I have noticed several of my non-technical friends using and began wondering. The conclusion that I came to is that, if you replace my IDE with something like MS Word and my text editor with something else, perhaps Photoshop or Illustrator, you'd get roughly the same workflow that I have, just without the code.

Now, I'm not saying that Spaces is essential, but I this is one case where something we think is nerdy, is actually pretty main stream.

Since were on the topic of application visibility and switching. I'm wondering if there is a better way than spaces. It's obvious that full-screen mode with easy switching isn't it. I find that context switch to complicated though I'm not quite sure why - way back when I was on windows, that was the way I did things. Perhaps expose is underused?

I just use Cmd-H and Cmd-Tab. I tried Spaces when Leopard came out and found it to be more trouble than it was worth.