Zero. gears are either installed correctly or they're not. there's nothing that a break-in period is going to accomplish. if you hear any noises from the rear end after you get the car back, take it back to the shop and tell them about it because correctly set-up gears will not howl or make any unnecessary noises.
When I went to pick up my car after I had the 3.73s installed, I got in the car and preceeded to exit the shop sideways and stay sideways through second. From that point on I have never taken it easy and I have had no problems. Roush97 is correct in saying that there is no break in period. Enjoy the gears!
I drove it easy for 200 then played with it a little for 200 and now I romp all over town. Maybe not nessecary, but I didn't want to chance it, too many conflicting opinions to blow an install because some one on the internet said its ok.
Thanks for the info everyone... I got about the same response from the shop... one guy said, about 200, another said drive outta here sideways if you want... I'll burn up the rest of this tank, then WHAMMO! The stomping shall begin!
I drove about 6 miles the night I finished the instal and did not hit it to make sure the gears are well lubed and to wear the paint off. That next morning I hammered it on the way to work, and WHOOAAA!! Big difference...now im used to it LOL. I suggest just getting a good 2-3 miles on them to make sure everything is lubed and working correctly before hammering it, although it wont hurt anything if you hammer it as soon as you get in it.