For what that coin? Any marketplace accept it?

I'm running poclbm and if I close my internet browser, the speed drops to 3,000 khash/s, but if I leave it open it'll be at 170,000 khash/s.

Is there a reason for this? Also, at this speed, how fast should I be able to finish a block and is there a way in which I might be able to go faster?