The iPhone simulator’s method seems magically wonderful. Since the iPhone OS is MacOS, all the kernel APIs are the same. The natively-compiled frameworks, libraries, and display engine are built from the same source code, so you know they’re the same too. And your Mac’s CPU is a lot faster than the iPhone’s CPU, so the simulator can slow down your program to iPhone speed, which is a lot easier than speeding it up (although admittedly imperfect).

via apenwarr – Why the iPhone Simulator is Awesome.