A friend of mine started using the Z back in the 5000D days (He used my 5000d when we were working at the research institute that Sharp gave it to for evaluation)
He is a busy and somewhat absent minded person, so he kept forgetting little details like there having been an important meeting that day, etc. He hated the Palm Pilot because of the handwriting recognition or lack thereof, but he needed something to help him keep organized.
Well, he got the 5000D with rom v 1.12 and never looked back. Upgraded to the 5500 with the original Sharp rom v3.1. Upgraded that to an 860 running the 1.4 rom translated. Upgraded that to an SL-C3000 with the 1.01 rom translated. He uses the stock PIM and Outlook XP, pushing the integration between the two as far as he can - he lives his life by the schedule and data stored on it every day. His Zaurus completely defines his productivity.
And he's never installed anything more complex than the PDF reader, and he wouldn't know linux from a hole in the ground. Besides PIM stuff he uses it for reading documents, taking notes, and listening to music and audio books.
The Zaurus can be a productive and easy to use PDA if that's all you're looking for. For those of us that want to put the work in it can also be our library, laptop, mp3 and movie player, handheld game machine, portable office, blackberry, telephone, and server.
Try that with just a PDA.