Mine is my laptop replacement when traveling. (Actually, I have it with me all the time.) I like to watch movies, play games, check email, read forums, and e-books in bed at night. I also like to try my hand at graphics, (though I'm not very good). I use it for taking short notes, and shopping lists, and find public hotspots with Kismet. I use the address book too. I bought TextMaker, but haven't really used it that much, as I don't find myself needing to do that much word processing on the go. When I do need to do real word processing, I'm usually at home and use the laptop. I've played with GPS and qpegps, but they are of limited use with the software being rather basic compared to commercial GPS software.
I have always wanted to learn programming for the Zaurus, but never really got too far with that, mostly being hindered by setting up a cross-compile environment. The second thing to hinder is the bewildering number of programming languages, and the fact (?) that it seems that even if you write a nice little script, you need to also use some other tool to write a front end for it. I read about some who compiled programs on the Zaurus, but they indicated that that was really slow.
By the way, welcome to the Zaurus community!