I live in Southern California and we had just one Sonic in the area - and the line for it has always been amazingly long.
Recently another one opened a few cities away, and they had to rent space across the street to give the line of cars a place to wait. I am not sure how things are going on the east coast, but out here, Sonic is just starting and people are loving it.
I live in Texas and travel to neighboring states every week. I have noticed in the small towns that Sonic is the only food buisnees going in a lot of areas. And they are always busy! As an investor, that's one thing I always watch, how buisness is doing especially during the down times. I have noticed a decline, yet that's everywhere I go nowadays, and in every buisness!