when I knew that our office was moving from York U to Erin Mills, I investigated the transit services.
1) GO Train from Danforth to Union, Union to Clarkson, MiWay from Clarkson to Erin Mills Pkwy and Dundas W. 2 hours each way, 2, or 3 transit services (if I took the TTC to Main station, or got a lift from my wife as she drove the kids to school) Cost in Transit: ~$350/mon.
2) TTC to Islington, MiWay from Islington to Erin Mills Pwky and Dundas W. 2 Hours each way, two transit systems, $350/mon.
Now, I spend about $200/mon on gas, plus maintenance and insurance for the car, but we have a second car when we need it.
And it takes me 1.5 to 2 hours daily round trip. Sometimes less, sometimes more (it has taken nearly 2 hours coming home a few times, but it has taken as little as 35 minutes, too!)
I decided it was better to Take The Car. :)