I have a run because that's how I started, with too many fears to let my chickens range freely. I got my first chicks in October 2009, and wasn't brave enough to let them free range until a month ago. I ONLY let them out of the run when I am home! And, actually, their "range" is just my entire back yard, which is very large (about a quarter acre). They don't get out onto the larger property on which I live; just stay in my back yard. So far. They haven't breached the back yard fence yet.
So, they're out every weekend, and every other weekend for me is three days. Sometimes I let them out when I get home from work in the evening, but that's not a regular practice yet.
My run is covered with bird netting.