I just wanted to preempt the inevitable threads about the drop in Karma last night. Let me explain.
First off, you may have noticed that Karma flatlined for the last 10 days or so. This was actually a bug and has nothing to do with the recent change.
Regarding the drop in Karma last night, this change affected every member equally. When the rating system changed, we had to change how the new ratings would affect a member's Karma. We used to combine all your ratings from Blogs and Pics/Vids into a score that got added to your Karma. We have applied the same kind of system, but now count the Up votes and subtract the Down votes.
The change is fair and proportional for each member.