In my own experience, if you're working outside peak commuting hours, public transport is horrible. Take a cold winter, services 20 minutes apart. One service is missed, cancelled, whatever, you're now there for 40 minutes waiting for your bus. Of course, you don't know that the service is missed, you're just waiting at a pole. And in my case, it was a connecting service, so repeat the process for the second leg of the journey. Sometimes it would have been just as fast to walk the 75 minutes home - though of course, there's no way of knowing from the outset.

My housemates were dyed-in-the-wool public transport users, the 'everything we need' variety, and then I went overseas for three months in which they had use of my car. On return, "we're getting our own car". Driving crosstown for a commute is faster than the 15-minute walk to the bus, the two-leg bus/train commute, and the 10-minute walk from the station.

Carrying your groceries on public transport sucks. Apart from a handful of cities, post-midnight travel sucks. Cancelled services suck. Being squished into someone else's armpit during peak commute sucks. Having to commute (walk) to your commute (bus) then commute again (walk) sucks when the weather is bad. Public transport with more than one leg in the trip sucks. Public transport that doesn't go where you want to go sucks.

Public transport is awesome and there should be much more investment in it, but there are a ton of reasons why personal cars are fantastic.