You know, they can take 1 GB of RAM, so there's no reason not to max it out, especially if you intend to run Mac OS X at any point (although 512 MB is adequate, for sure).
I ran mine with 1 GB, and it became quite evident that the main bottleneck was the video.
*thinks to self about getting the Pismo back...*
It really is a nice machine.
By the way, if you need any spare parts, let me know as I have a bunch of extra Pismo components I'd like to get rid of.
c