Much as I hate to commit thread necromancy, I seem to be having the exact same problem. Just got (yesterday, in fact) a Samsung CLX-3160FN and was quite disappointed with the Samsung-provided driver. The print quality with foo2qpdl is definitely better, but, as noted above, it's solely black and white. I've restarted cups (multiple times) while ensuring that it's set for Color.
Ubuntu Feisty 7.04 and the printer is network-attached.
As a side note, I would guess that Gutsy (which is due out within the week) has the most up-to-date version of foo2zjs/foo2qpdl. I don't know if that'll cure my problems, although I'm definitely hopeful.