The purpose of karma on any site like this (all the way back to slashdot) is to motivate people by giving them a measure of what their peers think of their contributions.
I actually have a plan for this. It's built into the current sw but not turned on. It hasn't been needed so far, and may never be because of Startup News's narrow focus.
If I reuse the code to make a general news site, as I've been thinking I might, I'll certainly turn it on.
