I'm going out on a limb and guessing from "Canadian conversion" and "skytrain" you're in Vancouver - which is great, because the answer is never! This city is great for non-car owners. I've never even bothered getting a license.
If I were you, I'd try to move closer to work though - that's a brutal commute.
Zikoris - one hour commute via skytrain could be in Surrey, which is not nearly so great for cyclists or transit users! I know that if I need to get groceries on transit, I need to go to New West (2 zones) which is faster than the store 2 miles away.
The times that I need a car:
1) Family shopping and errands -- car is needed a whole lot more post kids -- things like doctor's appointments, and lots of bulk groceries for family of 4, and home repair supplies scream "car" needed... as well, that "whole drop kids at daycare and still get to work on time" thing really impacts non-car users with demanding work jobs... but car is not really needed before you have kids..
2) Fun. The other time, is that we like to get out of town on the weekends. We go hiking/ camping / skiing and drive to grandma's 8 hours to the north, and to Calgary, etc. Note, Grouse by transit is doable from Surrey for skiing, however. Night skiing this way is awesome, if you start at 3pm.
3) Work.
I also need a car for work about 4 days a month. Without a car for work, i have to take the bus downtown, and then get a zipcar, adding 2 or 3 hours onto my day. Hopefully more car shares outside of vancouver zone will be available soon.
So -- if you have access to a car share, you would not need a car, even if all three of the above applied.