Personally I'm not a fan for my systems -- I've seen some cool paint jobs, but (other than my standardized RCA jacks for A/V connections) I for one prefer OG looking systems.
THAT BEING SAID, I've seen some fantastic results using Krylon Fusion spray paint. The tips I usually hear are "Multiple, thin coats" and "Prepare the surface well" -- which usually means wash, dry, wash again, dry again, and tape well