I use r121 (the latest available 2.6 kernel ROM) on my C860 with very few problems. I have 4bg sd card which 'just works', have been playing some games (glhack mainly), reading books (with justreader), reading pdf's (xpdf), syncing my mail & news form my home openbsd box (via ssh & rsync) & watching videos (using mplayer). I do a lot of shell scripting (I'm a programmer by trade & a card-carrying linux lover ). Don't do much with python yet, but have been meaning to learn. (ah, to have more spare time).
That said, there are a few annoyances. I haven't been able to get either my wifi nor my modem card working (yet). But my hardwire network card works, so I've been making do for now until I can get those running. My audio remote also doesn't work right now, but I know I have to get into some re-compiling of my own to address that problem.
So after that long winded commentary, would I recommend the 2.6 kernel ROMS? Definitely. The team is supposed to be releasing a new version too, soon. So if it doesn't work now, maybe it'll work tomorrow.
Most of all, have fun!