Something that I forgot to mention (kind of important). Normal radars are pointing to the FRONT, since the French have a point system and they want to be sure that the person driving the car is the one being docked points. So on a bike, no problemo. (however, they are talking about changing the law to make them rear facing again).
On autoroutes, very frequently you'll see one or two people on a bridge over the motorway. Slow down, they're cops, measuring your speed and phoning ahead to the next toll road. You'll be stopped there. If you see the cops on the bridge and where going to fast, I'd pull over and pretend you're broken down, and wait it out for an hour or so until they have forgotten about you.....
Secondly, last year a bloke won a court case against the cops when he was photographed going through a red light by an automatic camera. He stated that the law says that only a Gendarme can "see" a traffic violation being occured. hence the judge ruled that if a speed camera is placed anywhere, it will need to have a Gendarme posted next to it in order for a police officer to see the event, but can be assisted by a radar. To my knowledge that is still the case. So if you see some people close to the road, slow down.
BTW, for the newbies to France, on the Motorway that have tools (peage), you will always need to take the manned booths, ie, you can not go through the credit card lanes, unless there's a specific motorbike lane (to my knowledge, that's only on the A14).