I do it all the time.Actually I believe its safer than real wood.But remember not to be to close to it like don't inhale the fumes as they are filled with chemicals.

Sure, just don't cook any marshmallows over the fire.

Many people use them for starting the real wood burning. No harm in using them.

There should be no problem with doing this. Fake logs are compressed sawdust. Usually nothing more is added, but occasionally wax. Fumes from these logs shouldn't be much different than ordinary firewood. I wouldn't enjoy breathing them in, but I certainly would roast marshmallows over the fire. Duraflame says not to cook with them, but doesn't cite toxic fumes as a reason. Check out the links below.