I have a PP3. Opened it up, stick a 1Gb stick of memory in (it takes a standard DDR 333 SO-DIMM), then do some tweaking to bring up icewm and hang some useful stuff off the menus ... and it's basically a tablet PC running a slightly borked version of Fedora Core 4. Which is what I wanted.

With the 1Gb memory upgrade the PP3 runs OpenOffice 2.1 acceptably fast, and the screen is big enough for every dialog I've bounced off. It's not quite as good at stock Firefox 2.0 and Thunderbird 1.5 -- TBird in particular has some dialogs that are too deep for the 800x480 screen, and Firefox on Linux seems resistant to attempts to change the standard menu font to something that works well on a small screen. However, the basic stuff works (with a bit of tweaking -- it helps to know your way around a Linux system!) and with the assistance of a slim, lightweight keyboard with built-in pointing stick (originally for the Samsung Q1) it works well as a Linux UMPC workalike.

There's not really any comparison with the Nokia 770, IMO. On the other hand, if you don't run your life around PIM tools, the 770 *is* a pretty good competitor for the Palm TX, in all respects save speed -- and it's infinitely better as a web/ebook reader.