Yes, the idea that gnome is lighter than kde is a thing of the past.
cairo won't use much memory, but it does slow the desktop down
lsof -n /usr/lib/libcairo.s
turn off nautilus makes gnome twice as fast.
gconf-editor>apps>nautilus>preferences>untick show_desktop
oh yeah...and to start nautilus as brower
nautilus --no-desktop --browser
spatial nautilus
nautilus --no-desktop
do not use an svg icon theme (tango for example) or a cairo based theme engine...examples...candido, rezlooks, murrine, mirage, clearlooks-devel (cvs)
X+nvidia+gnome+svg+cairo=slow
exactly why? no one particular reason, but many it seems