I use fluxbox as my window manager and downloaded and installed gDesklets and then SuperKarma and found them to be very big resource eaters in fluxbox. Each of them eating up 10% cpu and 20MB of RAM. I actually compiled an entire gnome 2.8 tree just to check out gDesklets on fluxbox what a waste of time.
Then I came across adesklets, which only needs the tiny imlib2 library. Very good combination with fluxbox or any other light wm. It takes up nothing so you don't even know it's running. It is a very new project at http://adesklets.sourceforge.net/
. However it only has a couple of themes right now and the developer is accepting themes from people. If you use either of the two above I would advise you go check it out. I'm going to try and write a theme myself and send it in.