Yes. I wont be updating to IOS 6 unless there is a choice of mapping apps. I'm sure Apple maps will be a good product, but unless it's really as good as Google, or I can still install a Google maps app, then I will not update to 6.
I'm less concerned about transit and walking routing (because I am sure Apple will get there), but more concerned about search of maps. OSM search is currently nowhere near the level of Google maps search.
On google maps I can search for things like "usps near south lake tahoe" and it do what I expect. Try that on OSM, or anything remotely not a well formed address. Google maps has some sophisticated logic for biasing towards current location, and it knows the names of places, like 'moscone center', or 'facebook offices'. And of coruse, I cna mispel them all and it still find it.
If Apple maps can't do the same, then no matter how pretty the 3D view is, it will disable one of the main (for me) functions of the device.