I usually get 15, I got 5 twice in a row a while back but that's abnormal.
I think it has to do with the number of comments modded up, as well as the amount of moderation. Starting with +2 karma bonus, I can only get 3 up-mods, but with +1 logged in bonus I can get +4 for a total of 5.
If I'm in an insightful mood I usually have 2 or 3 comments at +3 (plus karma) at the same time, and 15 mod points. When I had only 5 mod points, I think I just had 1 or two comments at +1 (with karma to make +3).
Hey, screw this debate, isn't the slashdot code open source? I'm not looking, but if you want to know I'm sure that would help more than nerd fights. Don't get me wrong I like nerd fights, but usually when there's something to debate. Objective code isn't debatable! Except for Objective-C, lots of people object to it, hence the name. Right? I'm confused now, what was the question?