Their are a couple methods you can do to 'break in' a new tire. I keep hearing this 100 mile rule, but personally I see no need for 100 miles. Breaking in a tire involves gets rid of the shiny surface and to get used to the feel of a new tire. What I do is ride about 20 miles give or take, taking it easy with little lean to the curves and gradually build up the lean as the miles pass. By the time I'm done the 'chicken strips' on the edges will be about half an inch in back and the tires are then ready for whatever type of riding I want to do. Another useful tip is to go to an empty parking lot and do some basic maneuvers like figure 8's at various low to semi low speeds and a few panic stops. Also, rubbing your new tire's with a 'Brilo' pad and warm water just to get the shine off helps a lot. Doing this, allows no need to break in a tire expect only to get used to the new feel, IMO.
I'm usually too lazy to scrub off the molding release compound, so I just lean the bike.... Slow speed stuff, but trying to cover as much of the tire as possible. I've found the Continental Go's to have much more compound on them than any other tire I've ever run, and it took me a good 50 miles or so of commuting to get to the edge of the tire and make sure the entire surface has been cleaned by the road. Riding in the rain also helps.
I heard that fresh tires grip as good as new ones. That seems to be how it is in Nascar. I know back 20 years ago they used some compound to release better from a mold but now they do not use that.
Ive heard time and time again new tires being slick is a myth. My mind would still be put to rest by adding 50 miles on something before going hard on it. I have seen idiot dealer ships put armor all on ALL of the tire.
I have personally felt a new tire slip and slide knowing that it wasn't done up with armor all but straight from the factory. It seems to differ from manufacturer as well... My Conti Go!'s slipped a lot, the Avon Road Riders tend to not. Both were solid after 100 miles of riding or so though... I think more often than not, it's just a good idea to take it easy on new tires anyway...