I tried Xubuntu for the first time last night and was impressed. It ran great and looks better then Ubuntu. I cannot understand why Ubuntu's Karmic themes (boot screen, wallpapers, etc.) were so poor. Xubuntu's developers obviously gave more attention in this area. I know this doesn't matter much and can be changed, but to a new user a first impression is important.
I don't know much about XFCE. What negatives would there be in swtiching from Gnome for a basic user?