It needed a change, due to abuse and too much moderation work. So here is what we got:
Different "roles" affect author's karma differently. The higher your role is the more say you have. For instance, GURU's vote will give more karma to comment's author than "LVL1"

These roles give +3

• MOD - "MOD badge" Assigned by us.
• GURU - "GURU badge" Assigned by us.
• PRO - "PROFESSIONAL badge" Assigned by us.

These roles give +2

• EXP - "EXPERT badge" Needs karma +650 or higher
• ADV - "ADVANCED badge" Needs karma +400 or higher

These roles give +1

• LVL3 - "LVL3 badge" Needs karma +200 or higher
• LVL2 - "LVL2 badge" Needs karma +100 or higher
• LVL1 - "LVL1 badge" Needs karma +50 or higher

These roles give 0, but add to thumbs up/down count in comments

• SRC - "SOURCE Representative badge" Assigned by us.
• REG - "Regular user badge" Needs karma +6 or higher.
• BASIC - "Basic user badge" Karma -25 to +5.
• TROLL - "Troll badge" Karma -25 or lower.
• NEW - "NEW badge" Starts with Karma +1.
  NEW can not vote anything except if he has advanced to REG within 3 weeks.
  We need to make soure he/she is not here just to spam or troll.

Basically what we're trying to do is rank users based on their input and experience, not popularity.
You welcome to vote on comments to show support or approval even if it won't affects karma pts, it might attract attention from users that directly participate in user ranking.
Those that have enough karma to affect karma, I urge you to use the voting buttons responsibly!