I do!
I use the WebKit nightly builds as my browser - 'cos it's fast.
But you can't really assign WebKit to a space. Problem is, every time you update WebKit, Mac OS X sees it as a new application, so the last settings for an app called "WebKit" are thrown away for the new one.
It's a pain, yes - I am asked every time I open Webkit "Do you want to allow incoming connections for WebKit?" or something along those lines - it sees each new build as a different app.
Still, that's the price we pay for the world's fastest browser.😎