I let my chickens out as soon as I wake up until it just begins to get dark, when all of my birds will go back in on their own. I've started training them to go in the coop when I do because they know that's when they get fed, so if they haven't started to go in on their own, it isn't hard to get them to.
There definitely is a predator risk. I have fake owls and hawks out and I move them daily to try and deter the hawks and owls that live here. If you don't move them often, the predators start to realize that they're not real and not a real threat. I also have CDs hanging from tree branches and a pretty good rooster that warns the flock to take cover if he sees a predator.
Since managing my flock this way for about a year, I have had eight predator-related casualties. I lost one to a hawk first. Then a few months later another "went missing" and one of my other birds had two injuries on her back (she survived), definitely from a hawk, so I assume that's what happened to the "missing" one. Another one went missing with no trace after that. Then, we had a pretty uneventful few months until a few weeks ago something (I'm guessing a neighbor's dog) took five in one day. I think the hawk-casualties were mostly before my chickens fully matured and got better at hiding from them, and before the rooster decided to take on the job of guarding the flock, however, even a mature chicken can't always escape a hawk or take cover fast enough, and definitely is no match for a dog.
With that being said, I still free range. I've never seen happier chickens than free-ranging chickens. It is fun to watch them explore and search around for bugs and different plants to eat, and it saves a lot on feed too. I lock them up at night to prevent the nocturnal predators from getting them and have had no issues with night-attacks.
In the past, I have just had a pretty secure run with a coop too, not free ranging. What I have found happens in that situation is that we have an uneventful year or so and then something manages to get into the run eventually and the chickens are trapped inside and it's a 100% casualty rate from one attack. I figure, yes, there is a little risk every day when I let the chickens out to free-range, but when I keep them in the run IF something gets in (and something always inevitably has, despite burying wire around the run to prevent digging, double fencing, extra latches, etc.) every single chicken in that run is doomed. I'd rather my chickens take a small risk every day and be happy doing it than be confined to a run and then be trapped if a predator makes his/her way in.
That is just my experience and my opinion, however. Different things work for different people. 
