Is Mac OS X in a VirtualBox VM suitable for iOS development?
If this is a hobby and you are not planning on releasing any apps to the app store, and you can tolerate the slow performance and don't care about running on real devices, then don't worry about it. However, if you are creating a business the it is essential to run on real hardware. Any low end Mac (MacBook Air 11", is my current favorite) will blow away any virtual machine.

I have a fairly simple app that runs fine on my iPad and iPod Touch, but has all sorts of graphic anomalies in the simulator.