I've just started using GUIMiner v2013-13-03 at Slush's pool and have a couple of questions.

1. It's using a lot of my CPU, is that supposed to happen?
2. I'm getting about 245 Mhash/s with my GeForce GTX 780, is that good?
3. Any tip on how to improve the mining?

I'm thankful for any help you could provide, thanks.