You can do more than four if you manually edit the config file.
VUE was decent, but I’m still running WindowMaker on the desktop.
I tried eight but it was too confusing for my feeble mind. :-) Having just four fits into my comfort zone. It seems that four is widely used since I think it's the out-of-the-box default for GNOME and KDE. As I mentioned elsewhere in this thread, I become accustomed to having Firefox on desktop 4 with xterms open on the other three.