I saw this creep up on a mailing list, and it never really occurred to me that there really was a difference.  But there is.  Anyways a simulation is done 100% in software with no hardware assist.  While emulation has some kind of hardware component (Originally it was microcode on the IBM 709 to run IBM 704 programs).

So there you have it, programs like SIMH, Qemu are simulators, while programs like KVM-Qemu and VMWare are emulators.

Hope that clears that up.