I've recently converted my 32Mb iPaq to Linux (familliar). The Perl distribution, works and appears to fit in less space than Python. It comes with GTK.pm and core files. The only reservation I have at present is that perl -de0 doesn't work as it can't find dbperl.pl.
If you can code your own PIM tools and do without WinCE's utilities it is possible to run Linux, Blackbox, Bash, ssh, msql, vim, a web-browser, irda modem and Perl in the palm of your hand. Administering a Linux system on 16Mb (the other 16Mb is wiped on shutdown) is an enlightening experience.
There is Perl for WinCE, and it works well... but WinCE lacked the configurability of Linux. The conversion process from WinCE to Linux is daunting at first, but pretty easy to follow and only one stage may reduce your iPaq to an expensive paper-weight, however this can be rectified (apparently :), it is possible to return to WinCE too. There is also a cluster of ARM servers to compile things on, if you require C libraries and stuff. I'm impressed.
Is is practical to code on an iPaq? I can't say. My hope is to write bespoke tools for stuff I want to do, and load the scripts to the machine across the network. Typing things Perl on an any touch-screen organiser will be fraught, unless anyone wants to collaborate on developing and alternative key-binding for xkbd or some such? It is fun oh yes:)
Are there any more iPaq Perl hackers out there?