All my cats have been indoor/outdoor cats. It's usually better to let them out when they are younger, so they get slowly used to the outside world, rather than when they are older. Bubbles couldn't get out of the garden until he was old enough, as I have a 6ft fence all around it. Now he is bigger, he jumps over it no problem.
If you do let them out, let them out via your backyard, not the front door (near the road). They will probably stay very close to the house for the beginning. And call them regulary and give them a treat, if they come home straight away (coming home straight away can mean 10 minutes for a cat!). Never close the door on them while they are out, they need to be able to run back home if they get spooked.
I prefer to let my cat out at night rather than the day, as there are less children and dogs about, but we do not have any racoons or other dangerous animals here, it depends on where you live really. English City Foxes are no threat to a cat, they generally ignore each other.
Oh, and I live in London.... so yes, we have plenty of cars about, but being a city, it's generally slow moving, so safer for a cat than fast moving country traffic. In Germany my cat lived to the ripe old age of 19 being indoor/outdoor. I couldn't imagine keeping a cat indoor only, my furniture would be shredded to bits, the fence outside looks bad enough!