By default Knoppix 3.3/3.4 feeds
vga=791
to the kernel, which virtually everywhere I try results in an alarming and user-unfriendly
"You passed an undefined mode number"
error message.

(See lots of discussion at
http://www.knoppix.net/forum/viewtopic.php?t=4625
)

I've tried just leaving this out of my isolinux.cfg, and it seems to work fine.
But the Knights Who Made Knoppix must have put it in there for a reason...

What downside is there to just leaving the thing out so that my users don't get freaked out by the error message?