Positive rep. doesn't seem like a bad idea, the problem arises really when people start dishing out negative rep. Some people take it seriously some brush it aside, to be honest I don't its up to members to decide who should get negative reputation that is the job of the Administrator or Moderator (to punish if need be e.t.c.). But for saying thanks for doing stuff I feel its perfect.
You always get a nice fuzzy feeling inside you when you get a bit of +ve rep... or maybe thats just me. :erm: