(moved about 18 months ago) and am here at the moment, too. A few thoughts:

* If you have kids, Manhattan can be tough. Apartments are tiny and outdoor space is scarce
* Things you'll have to value to make the move worth it: dining, entertainment, cultural opportunities, the fun of exploring, walking and the general energy of being surrounded by a lot of people
* Relatedly, New Yorkers get a worse rap than they deserve. Pass them in the street and they don't have time and will often get annoyed by people who get in their way or slow them down. But that's no different from how people get annoyed at inconsiderate drivers - the sidewalk is their freeway. Ask them for directions or something, and they're happy to help out. They just won't stay and chat - no time for that.
* Things that, if you value them, will really make the move tough: quiet, open space, casual relaxed environments, driving (give up your car if you're living in Manhattan, it's 10X more hassle than convenience), eating dinners where you don't overhear every nearby conversation
* You can't be a cheapo in Manhattan (and not implying that you are at all). Everything will be expensive, and your apartment will be tiny. Manhattanites like to say that the city is their living room, but that means you're going to go out a lot and spend a lot. If you're not willing and able to do that, the tradeoffs for living in a shoebox apartment are hard to justify.

I loved my time in Manhattan and lived there for 10 years over a span of 15 years, and was very sad when I left, even though it was time to move on. But it's surely not for everybody.