[GFischer]

I'm not PG but I remember reading that it was a sliding scale based on the average karma... so if your karma grows slower than the total karma, you might have lost the ability.

I can't find the interesting link with the analysis I read it from (it was from around the time PG removed the points), but there's some confirmation here:

http://jacquesmattheij.com/The+Unofficial+HN+FAQ#cantdownvot...

[chc]

Yeah, the thresholds are constantly creeping upward. I don't know what they are now, but I'm pretty sure they're somewhere above 600.