Yes, Spaces is very nice. I have 9, usually all loaded with stuff. Right now, I have four Firefox windows with multiple tabs in the center middle, two Safari windows with tabs in the lower center, email in the upper right, 22 Quicktime windows in the center right, VLC in the center left, iTunes in the lower left, and a game in the lower right, and an OpenOffice presentation in the upper left. There are no responsiveness issues. If you were encoding video or something similarly taxing, then you would see some slowdown with out without Spaces. By the way, did you know that you can set applications to always open in a particular space? Also, make sure you assign a hot corner to activate Spaces!