I think here in MA you only get in trouble for double the speed limit. I've been pulled over 8 or 9 times last year alone (80% of the time it's for 25-30mph over the limit) and I always get away with warnings (except once in upstate NY where I got a ticket for 30 over which resulted in a $700 ticket that the lawyer I hired online turned into a $220 parking ticket with nothing on my record

)
If traffic allows, I never ever drive below 85mph on the interstates around here (speed limit is 65). I've been passed by cops while I'm doing 88mph and they never bothered with me. I'd say on an interstate, 80 in 65 is considered "doing the speed limit" around here (most traffic goes at around 75-80). I tend to cruise at 90mph.
I never exceed the speed limit in populated areas tho because:
1) it's retarded
2) small-town cops are generally a pain in the ass