How many rounds are in Horde? Do the enemies get stronger?

There are 50 waves, and in later waves the enemies will get modifiers such as double health, so coordinating fire and active reloads become a very big deal. I think Horde is the dark horse of Gears of War 2, people are going to be surprised by it.

What happens if you clear all 50 waves?

Honestly, I don't f*cking know. I've only gotten to wave 40! You totally caught me there -- I need to beat it before we ship.

Is there anything to unlock, or any secrets that tie into Horde?