Coming from a city where public transportation goes EVERYWHERE, I was quite the happy camper when taking full advantage of the subway system in Toronto. The system is pretty intuitive, so it's easy to get around the city. If you're here for more than a week, be sure to pick up the week pass (it was around 8 USD last time I was there). What's even better is the buddy system - buy one get one free deal.
Expect incredibly clean stations and trains. The Canadians know what they're doing!