We have a fenced yard so they all go out there without a leash, but if the area they are going isn't fenced I always have them on a leash.
Buster is the exception as he is never more then a foot away from me. So with him it depends on where we are. If we're in our yard, but outside the fenced part he is still off leash. If I take him to someone's house (usually my parent's) he is off leash. If we walk down the road or somewhere like that I have him on a leash.

No I don't trust my dogs 100% off leash (other than Buster), but I have had a "test" with all of them and they passed. One time I went outside and the door didn't latch tight behind me and Bitsy and Charlie ran out. Bitsy just ran to my neighbor who was outside and Bitsy loves her to pieces. Charlie started running down the side of the road. I yelled "Charlie sit!" and he sat right down and waited for me to come get him. I was very proud of him.
Another time I was mowing the yard and stupidly left the side gate open. Went Justin and I took the dogs out a little later Charlie, Bitsy, and Buster stayed in the yard, but Nacey and Nova ran out of the gate. I was very proud of them as I called them and they both came running right back inside the gate.