Yes, it unlocks a "coupon" on the screen when you check in.
The coupon has an expiry time set also,
Don't forget you (unless you're rather intelligent enough to hack the service and your phone, not impossible ;)) need to be stood in the close vicinity of the check in point (i.e. the entrance plaza!) to succesfully check in.
You can check in friends that aren't there however, so they can gain entry. But I'm guessing they ultimately need to be present when you redeem the coupon at the cashier/turnstyle, and we have no idea what the expiry time on them will be (they might be 'cruel' to stop people cheating and set it to like an hours expiry or something, as technically you should be there when you check in anyway!).
They can also limit the deal to one device check in in 24 hours or even one time only, which I'm guessing they'll do to stop people passing their phones around. Then again, they might not :P
Also the hotel thing - I can only think they'll either have another places check in for it (as you can limit Facebook Deals to the first 100 customers for example, but its still open to cheating, unless the expiry time is really low!), or, what might seem the more sensible route for them would be the first 100 people through the turnstyle to claim it at a certain point after the turnstyle. (i.e. first 100 people in a line after they are through the gate!).
I guess we'll find out soon enough though :P