Another idea:
As far as I remember Karma has built-in time-delay, so if I double-applaud Kit I'll get "
Sorry, you can't repeat a karma action without waiting 1 hours." message.
Increase the time delay to 672 hours (that's a month).
This way if people gonna try abusing it - it will be be only one vote per month, so no big harm done. While the system would still play the role of indicator of who people like and who they don't

(cause that's what it suppose to be I guess, opposite to "Thank you" which shows how helpful the guy was) Cause currently the Karma system is only yet another indicator on how old member you are - it's quite obvious that older members got more Karma and newer got less. Karma also duplicates the Thank You system - last... 6? Karma points I got were given to me along with Thank You so I have no idea what for this is anyway....
Perhaps remove Karma at all than? If there's no negative Karma and it duplicates other stuff we have already?

What you think guys?