Agree with everything others have said already. Will try not to repeat all the excellent points, but will raise a few other points:
Different people react differently, and it's very important to tune into your passengers. I've done steep turns with several passengers, but only after we've spent 1/2 hour or so flying and I've noticed that they seem perfectly happy with the sensations. If there's any doubt at all in my mind, I'll keep turns to 20 degrees of bank.
Keeping passengers busy helps - it stops them from bugging you, keeps them happy, and it might even help your flying! Having an extra pair of eyes looking for traffic always helps. I wouldn't give my chart to a passenger on a route I'm not familiar with - but if it's a route I've flown several times, and I know I can find my way without the chart, the passenger might (depending on how interested they are!) like to follow on the "map", and you could even delude them into thinking they're being a big help by pointing out roads/towns to you! (If your passenger is a pilot, however, it's completely different - then you can trust the passenger to navigate for you.)
You asked about giving passengers control. This is legal, but is it sensible? I have done this on occassion. I have never promised anyone they can have control, or even mentioned the possibility, until we've been flying for plenty of time and I'm ready to give them control. Even then, I'll only do it if the weather is perfect, if the air isn't too busy, if we're well away from any controlled airspace, if the passenger has demonstrated that they're totally happy with the sensations of flying, and if I'm sure the passenger is a responsible person - a list of requirements which aren't satisfied all that often! I've heard enough horror stories from instructors to know that I don't want to get into the situations which their job forces them into from time to time!
Even then, I'll only let them play around with the ailerons, after a "trial lesson"-style demonstration from me - there's too much that can go wrong with any other control as far as I'm concerned. But I will hapilly demonstrate how all the controls work if the passenger is interested (most aren't, but some are!)
One other thing which no one else has mentioned is flying with pilot-passengers. This can be great fun. You know that the guy sitting next to you will be a good passenger before you start. You can share the duties, which takes away some of the stress and leaves more time for enjoyment. It's fun, for example, to have one of you navigating and the other flying for the first leg, and then swap over for the return leg. (But don't let the passenger take off or land unless they're current on type.)
The most important thing, after safety, is for your passengers to enjoy themselves. The next most important thing is for you to enjoy yourself!
FFF. .---------