It works, but it's not as lightweight as EDE (Equinox), WindowMaker, Afterstep, and so on. Granted, the more you want lightweight, the less features and integration you will get; and conversely, the more features and integration you want, the less lightweight it will be. Granted, if all you wanted was a very lightweight environment with tons of functionality, you could always use something like
5dwm, but I suspect that most people would find this to be a bit on the ugly side of things.
As a halfway between the large destop environments and the barebones window managers, Xfce does pretty well, but I tend to get annoyed by little things about it. And I don't actually think that it's very lightweight... but maybe that's because I only ever use old computers that make Gnome and KDE feel too sluggish. I don't know. Maybe I'm just rambling.