Do they come with a reward of some sort, or is it strictly for bragging rights?
Steaks earn you lingots, which are Duolingo currency.
What is a lingot?
A lingot [ling-guht] is the Duolingo virtual currency. The more you learn on Duolingo, the more lingots you'll receive and be able to use in the store! They can be earned through:
I.e. 10 day streaks Earn 1 lingot for every 10 days on a streak (1 for 10, 2 for 20, etc).
You can exchange them for stuff in the store to help you while you practice. http://www.duolingo.com/show_store