Here's an easy one:

What’s the difference between aTV Flash and MiRow?

I’m in the process of jailbreaking my new aTV2 and setting up a NAS, and I’m wondering which I should buy.

As I understand it, MiRow is a Mac application (and is not Lion compatible anyway), not one for the ATV2? That should make your choice easy - ATV Flash (black) is what you will want to use on an ATV2.