SuperKaramba can also be taken from the package manager, or downloaded from their site. After the download and installation you can start the tool from the terminal with superkaramba. It will probably also be in your start menu, but that wasn’t the case on my Gnome based distro.

After you started SuperKaramba you can click the New Stuff button to get new widgets. There is a nice list of widgets you can choose from in that list. There are also sites like KDE-Look.org and Biodesign that have some widgets on their site that you can install. After an widget is installed you can click the Add to Desktop button after you have selected it, and the widget will appear on you desktop.

I like SuperKaramba more then gDeskets, it has a more modern interface and it has a bigger user base behind it.
But the fact that it isn’t completely native on Gnome makes it a bit “unstable” at times, so if this bothers you i advise to stick with gDesklets.