Hello Dr.,
I am a bit late in this thread since i haven't been reading the list for a few days, however, as a long time PDA user (starting from one of the earliest casio digital diaries, to casio PV, to a palm III, to a palm lifedrive to my present nokia n810), i feel your pain.
If you are looking for a good no hassle PDA, mainly for PIM purposes (like you listed) as opposed to a PIM+Media manager (for mp3s, video, ebooks, ...blah, blah), I would recommend getting a phone instead of a PDA. I have heard good things about the motoming, tho' i can't comment on it since I don't use it.
I also have heard good things about the Nokia E71.
Now, if you /do/ want a PIM+Media manager+a palm sized proper linux system, I'd suggest investing in a Nokia N810 (or the discontinued earlier version N800)
http://www.nseries.com/products/n810/#l=products,n810 http://en.wikipedia.org/wiki/Nokia_N810
These run Maemo desktop: http://maemo.org/
It *is* expensive, but you may find cheaper resale pieces on ebay. Also, once you have the n810, although you would be able to sync to linux natively (in fact you could also use the very same applications on your desktop as well as the pda -- the gpe suite[1]), you'd find it more convenient to sync to something like google calender if you so wish.
If you have questions, i'd glady answer them since i tend to use my n810 a lot.
regards, - steve