Is it possible to have both an iOS app and Mac app in the same project?

As the title says, I'm wondering if it's possible and reasonable to have both an iOS app and Mac app in the same project. That is, an Xcode project that has a Mac app target, and an iOS target.

If so, what should I watch out for, and is this even a good idea.

A little context: I'm working on a client app for a web-service, that will share a lot of the API connection (model-layer) code between the iOS and Mac platforms.