There's certainly the scope to do these things, there's just not that much screen real-estate to use (that's my problem with applets anyway). Perhaps we need some sort of parent applet which can be used to quickly select which of its children to display.

The Chumby stuff looks quite fun, the applets themselves are Flash, I don't know whether the applets are open-source, but it ought to be possible to write a flash container app to sit on the desktop and do something similar (perhaps even with the same code). Might make the rest of the system rather slow though.