If you want a comprehensive system monitor without the hassle of gdesklets, you should try out <a href="http://conky.sourceforge.net/">Conky</a>. It looks awesome if you can configure it right.
Yep, look at mine for example. You can pipe-read any plaintext you want. I wrote a Ruby parser for Yahoo weather for example. And I read in the calendar via the cal command, and I fetch my external IP address via a script on my server, etc.