I own a Ben Nanonote. Note taking isn't one of the things I'd to use it for. Pen and paper will be faster :)
This thing comes with GNU Octave/Gnuplot, Emacs, MPlayer plus a host of script languages: python, lua, guile, tcl gforth, here's a (incomplete) list of applications including screenshots:
It won't compare too favourably to a modern smartphone, but I keep to think of it more as an open hardware platform/devboard than a consumer product. BTW for hardware hacking you can easily connect 6 I/Os (3.3V TTL) via the UBB (http://en.qi-hardware.com/wiki/UBB).