I use it to transfer files from PC to Wristwatch,
Apache/PHP Webserver,
Hacktool for auditing my network, (Need a new wifi card before I can seriously use it for this),
All my music is played on the Z,
Gaming, Via SNES emulation,
Scientific Calculator with gwCalc,
Web and Email over GPRS,
Image Viewer,
Wireless COMMS tool,
Circuit Simulator,
Writing Word and Excel Documents,
Reviewing presentations,
Reading any highly-graphical PDF's (Text based docs like Z4CK and Digital Force get put on my WristWatch),
PIM!!!!!! (Shocking, I know.)
GPS system,
Writing Code in Text Editor,
Instant Messaging,
Databases (Portabase, zElement, zPDG)
Web Development,
Simple Image Editing.
Basically, the 5600 can do everything except sensible video playback. With Kernel 2.6, we should even have that!!!! ^^ (yes, it's VERY fast.)
So for now, use what you like. When OZ-OPIE/2.6 is fully functional, then use it. It's going to be very worth it. ^^