Cam I know Kelly's and actually I am surprised by the number of people I have met that know it too even though they were not raised in MA. I go everytime I am home but usually to the one on Rt. 1 in Saugus now since it is Dec. and very cold at the beach.
As for after my prom many many years ago, a group of us were starving (since the food was so good at the prom...note read previous few words with heavy sarcasm), so we headed off in search of food and somehow ended up at a Ground Round in the Prudential Center (its no longer there). We all ordered food, danced on the dance floor (they had a DJ that was just loving us) and dragging other diners out of their seats to make it "their" prom night too. We were the hit of the place. We ended up staying there til closing eating popcorn, singing, dancing, talking with all the patrons etc. The manager told us it was one of his best night and that the staff was just so happy we were there. We were crazy and having the time of our lives and everyone got caught up in it. After we closed that place, we did end up at the beach for a few hours hours and then at about 6am we all headed to the howard johnsons (the resturant not hotel) at Wellington Circle in Medford (also no longer in business) and had breakfast...then we all went home to crash.