I was at the Yonge / Lawrence Burger's Priest location today for the first time. As others have noted, it's small. There is a small amount of counter space available for people to eat, but when we arrived (around 1pm on a Tuesday) the seating was almost entirely full.
I got the Pope burger (one of the many "secret" options) which is two patties and "the option" (the cheese-stuffed mushroom). I think one of the blessings and curses that BP received was its Zagat selection. People come in with sky-high expectations and are disappointed. I tried to keep my expectations reasonable, and was entirely satisfied with the burger. It wasn't gigantic but it was big enough for me and it tasted great. Some people may not like the mushroom-cheese "option" but I really enjoyed it. Next time I'll try the Vatican (grilled-cheese sandwiches replace the buns). The fries were okay (normal burger joint fries).
The service was fast and friendly (although I probably went at one of the slower times of the week). The only reason it loses a star is the price. My total for the Pope burger and fries (no drink) was $17. That's pretty pricey, but even so I'm sure I will return :)