The only non-windows stuff for the Karma right now is Mike Schrag's "Rio Music Manager Lite" and "Rio Taxi Lite". They only work on ethernet.

And to counter Mark's comment about slow ethernet speed: The dot-release that will be available soon, should theoretically improve ethernet speeds quite significatnly. But at the moment, yeah, ethernet is kinda slow (took overnight to fill my player) and USB2 is hella fast (fills the player in a surprisingly short time, IIRC something like an hour or less).