Disclaimer: I didn't use OSM's default/ugly color palette.
Disclaimer #2: I have used iOS 6 maps, and the most visible change (other than the color palette) is that subway markers are clickable and that Yelp is more tightly integrated into the pin details.
Without knowing more about your web site I can't do a detailed comparison, but unless people use your web site every day, on the move, to search for transit, business and social locations then the use cases just aren't the same. Not to mention that the biggest issue with Apple Maps is the dismal coverage outside of the US.
If I had to use the same system to actually route myself from place to place, it would drive me insane. As an actual mapping product, Google Maps is peerless.
For Apple, they just need to license more satellite data, which they no doubt will. Google maps satellite coverage was pretty sketchy in the early days too.
Not a dealbreaker, I guess, I'd just be mildly annoyed if I lose that