I freaking loved this place so much I came both mornings I was in town on the weekend. The one downside - they ran out of iced coffee. BUT - the hot coffee was one of the best I've had in a long, long time.
The ambience of this place is just as lovely as the food. There's lots of natural light. There is a good bit of seating, but since the place is quite busy most of the time, especially in the morning, it may take a bit to actually get a seat. Service is great - I was treated nicely by the people behind the counter both times I went.
The coffee and espresso here is fresh, reasonably priced, and just tastes good. The roast is not too bold yet not too light. I wish they had fat-free milk as an option though.
The pecan square I had was absolutely delicious. I've been looking for some good pecan pie anywhere in the northeast US, yet this pecan square is the closest thing to a real southern pecan pie that I have had in a while. I forgot how much it was, but it's so worth it if you have a sweet tooth and can afford to eat probably the equivalent of a stick of butter in the square :)
The cheddar jalapeno scone was also delicious, though it didn't have as much of a kick as I thought it would. The outside is crunchy and the inside is soft. Yum.
Dineen's Coffee is definitely my go-to spot when I'm in Toronto.