CS5 does not work in spaces. Like another user said, Adobe makes no effort to make any cs5 apps behave like a mac app.
I activated spaces and assigned FW to space 3 and DW to space 2, and soon as I toggle betweent the two apps, fireworks moves to space two. And that's just one of hundreds of gripes against Adobe software. Half of the scroll windows in their panels don't response to mouse scrolling, preference commands are NEVER correct nor are many other mac system commands. Adobe has become a company I love to hate. They ARE the new Microsoft. I bought CS5 hoping that many of these issue would be fixed from CS3. Pretty much the same BS. If and when an althernative comes along, I'll just ship immediately.