This is funny, as I was just mentioning to a friend that I couldn't live without it. I have 9 spaces, 4 with dedicated apps; the rest empty and ready for projects. One I have setup to convert txt/pdf's to ePubs - several Finder windows, Text Edit and Calibre. I can go about my business in other Spaces - then go back to work converting books and never lose my layout.
(btw: I have Spaces setup to use my UR hot spot. That way, I can drag/drop items between Spaces (also, it's easy to swap Spaces).)