I wouldn't say President Obama is Ben's most famous visitor. That honor seems to have been given to Bill Cosby a long time ago (he always eats free; President Obama was offered the same courtesy but opted to pay for his meal).
As for the food, it is good. It may take a few days until you want to go back, but if you're visiting DC, make the trip up to U Street at least once. Ben's is right across from the metro.
While you're there, Cake Love is a few blocks west. Their Love Cafe is a great place for dessert.