It doesn't take much karma to vote or flag. Well under 100 points IIRC. Past that point, having more karma has no effect on what you can do on the site.
>>twblal+(OP)
Correct. Flagging takes 30 (well, 31) and downvoting takes 500 (well, 501). After 250 you get to set your topcolor. I think that's about it for now.