Well, I don't know about Toronto, but I can tell ya how it goes in Chicago.
Pros: Tons of music venues, amazing bars, restaurants, great women, jobs, public transit so you don't have to drive everywhere (could also be a con)
Cons: Extremely, like crazy, expensive compared to suburbs, parking is an enormous pain in the butt and expensive, if you go to the wrong part of town there is crime.
Those are the big ones off the top of my head, although you'd be surprised how frustrating parking is. If you come home at the wrong part of the night you may be circling for an hour before you find anything. You can rent a spot in a garage for $300/month.