5-10 over in the city, 5-15 over on the highway depending on traffic, time of day, which highway, etc. I try to go right at the limit or 1-2 over if it's a school zone.

I've gotten tickets for going this much over:
13mph (city)-age 17
15mph (city)-age 18
18mph (highway)-age 19
16mph (city)-age 23- didn't realize I was in a school zone. I was only 1mph over the regular speed limit.

One speeding ticket in the last 5 years isn't too bad.