Excellent. I do the same with the State Troopers and the local Cops when in town.
On the Highways the State Troopers will sometimes be going 5 MPH below the posted speed limit, and every driver that can see the patrol car will slow down to that speed. I have no issue passing the black and white as long as I am at the posted limit. It's nice because you usually have an empty highway once you pass the trooper.
In the city, the cops will always be going about 10mph sometimes 15mph above he posted limit. I tend to slot in behind them, at a reasonable distance and follow at the same speed. Hey, if they don't have the lights or siren on, they should also obey the posted speed limit. If they want to give me a ticket, they will have to explain to the judge why it's OK for them to speed when they are not on a call.
I did that one time. As soon as I got past the cop he zoomed across three lanes and got right next to me - about a foot from my door. I looked over at him, confused, and he jumped in behind me - about a foot from my bumper - and turned on his headlights, spotlight and flashing lights. Thus blinded, I pulled to side of the road. The cop got out a loudly berated me for being so "disrespectful" as to pass him. He them wrote me a ticket for 5 mph higher than my cruise control was actually set for. That extra 5 mph was actually the lowest ticketable speed. He wrote on the ticket that I sped past him and looked at him (which was actually me looking terribly afraid and confused when he almost side swiped my car).
That little bit of cop ego cost me $90 and a morning in court.