If you haven't heard about the site YouCity or checked it out yet you should take a look. The YouCity team has been diligently working on mapping and modeling Manhattan.
The website is actually a social networking site with a 3D map that is displays information on entertainment hot spot in the city. It seems like an interesting concept (social mapping service?) The map really reminds me of SimCity 3000.
I spoke on the phone a couple of months ago to the man behind YouCity, Shu Zang. He told me each building is individually modeled to accurately represnt the area. Now that's detailed dedication. I'm not sure how many people are modeling the buildings but it must be a lot since Manhattan has so many buildings. Also, there are a few inaccuracies and buildings that should have more 3D detail added to them.
Though, I don't think every single building in Manhattan is modeled and it would be nearly impossible to do that. Nonetheless, it's quite an amazing project and demonstrates an interesting application of how 3D mapping can be used in other ways.
You can find more out about YouCity 3D Maps and how they develop them maps at youcity.com.