My friends went last week and walked up and got a seat no problem! I think they had to wait 15 mins but got a seat! I also heard that the place was booked up the first few weeks and its probably true! BUT I also think what happens with a lot of this stuff is people simply cancel or a lot of no shows and so they probably get a lot of last minute seating as well. And this restaurant is pretty big, being able to seat 250 people so if its just 1-2 people, they probably can accomodate people at the last minute. If its 5 or more, then it may not be so easy.
Anyway the question been answered, yes you can go to the restaurant without reservations, but the chances of getting in will probably depend on the day and long people are willing to wait!