I have been to Cornerstone several times, twice for dinner and a few others for drinks and snacks. A friend lives walking distance down the road and it is a great option if you are in Aspinwall and want tasty food and outdoor seating. Last time we visited they even had blankets at every table since it had gotten a bit chilly in the evening.
The food is good- nothing out of the ordinary but good ingredients and prepared well. My first dinner there I had the lamb burger and sweet potato fries-- you could put goat cheese on almost anything and I would be a happy camper. Second time I opted for the soup of the day- a delicious smoked corn soup- and the duck taco appetizer as my entree along with bread pudding for dessert (I typically avoid dessert but it was a little bit chilly outside and this really hit the spot!).
While the food is good, it is overpriced. $13 for a relatively small burger and fries... $20 for my soup/tacos/bread pudding (and those "tacos" were super small) plus another $5-6 added on to each for a beer. I'm all of 5'1" and don't require huge meals, so for these prices I should be able to fill on up!
The atmosphere at Cornerstone is great and I am sure I will continue to stop in with my friend from time to time, but there are definitely better places to get more bang for your buck!