Hm hardly. The average linux user is something like 100 times more skilled, computer-wise, than your average windows/mac user. That's why IMHO it's highly unlikely that a Linux Desktop based malware will ever reach big numbers. Those linux people are mostly geeks, they can tell easily if something is going wrong...
I disagree.. If linux had a larger market share you'd see users that weren't '100x more skilled' and advertising a cleanup program would be viable.
Permission structure of *nix is the same, and fools can be fools anywhere. A 30% market share for linux doesn't mean 30% of computer users gain 100x the skill overnight.