Yes, I think there's some specific number or plurks per day you have to do to maintain karma

I think it just expects you to make at least one plurk a day to maintain the status quo. With more being good (up to a point)

I think Karma is like the movie speed, keep posting at a certain rate or BOOM. . . bits of text go flying

there are 6 karma periods in a day, I think it starts going negative after there's a period of no plurks or comments from others on yours

or your comments on others' plurks

as long as you plurk, comment on a plurk and receive a response on your plurk every period, you get full karma.

Wow thanks!!!!! This makes total sense. I am going to keep the image of an exploding bus squarely in mind and try to be more consistent.

if NASA is used to add up karma points

I think you're right, ryanS!