Garry puts forward good reasons why not to buy a desktop RISC OS system: I'm pretty certain my Iyonix will be my last one. But I think he is actually making a better case for using VRPC than for porting RISC OS to a PDA.
I'm quite certain that my next desktop computer will be an iMac. I already have a copy of VRPC running on my old iMac and it is a very pleasant way of using RISC OS. And when I want to do something that RISC OS isn't good at I can switch to MAC OS on the same computer.
My main uses for a PDA are word processing, spreadsheet, and MP3. I admit, I would like to have Techwriter/Easiwriter on my PDA, but the spreadsheet on my Palm PDA is better than anything available on RISC OS. And I don't believe a RISC OS MP3 player is going to be any better than the one on my Palm. The latest generation of Palms also do Sat-Nav. I just can't see how RISC OS can compete in this market.