The old Apple TV didn't have much interest behind it. With iOS powering the current one it has a much larger pool of developers able to release code for it. It also means it will be trivial to port some existing apps to run on it - the biggest obstacle (IMO) is the user interaction/input.

if someone is going to try and write something from scratch targeting the hardware, they're going to fail. If someone writes a thin layer utilizing the existing video APIs, then they'll be in business.

Without any hacks the Apple TV will sell more units. With hacks it can make for a better system. Not saying necessarily that it will, but it can. The number of people willing to hack such a device is only a small percentage of total owners, but it could be close to the number of people willing to run the existing Boxee software. I'm almost tempted to include Boxee Box, but I think they'll get a good amount of new customers with that product. They won't do large scale (Apple, MS, etc..) volume by any stretch of the imagination however.