remembering where you are in the playlist: every time i hit the playlist button, it takes me to the top of the directory tree. is there any way to get it to pick off at the last point i navigated to?

If you're using v2.0b7, you can press the down button once to highlight 'Playlists'. Holding it down then takes you to the same place you were in last time.

At any playlist level, holding the down button allows you to 'insert'/'append'/'replace', as with the search screens.

is there a way to speed up scrolling through directory items. on my NEO, if i held the scroll key pressed, after a few seconds, all the directory items would start flying. this would let me get to a general area real quick, and then slow down to select the playlist i wanted.

You can use the alphabetic buttons on the remote to skip. Otherwise, the wheel should go pretty quickly.

...My "master" mp3s are on my desktop (windows 2000), and i would like to "sync" deltas to the RIO...

I'm hacking on something like this in my copious spare time. Don't hold your breath, though.