Nick - as Cakey said, French roads are great and a pleasure to drive on.
Getting out of Calais or Boulogne is an absolute breeze - really clear signs and easy to follow. Ouisterham/Caen can be a little more stressful but keep calm, realise that you need to travel a little bit in the "wrong" direction if heading South and you'll then pick up the road that takes you towards le mans and on to Tours..and it's all fine. Le Harvre + St. Malo - no problem. Never done Cherbourg so can't comment.
Never been stopped by the gendarmes but they can be out on force on the way in/out of ports so make sure you have got every thing. Lots of the French drape the flouro tabards over the front seat backs - good idea. get all these things from your local Halfords or similar well in advance cos the prices for this gear at a channel port is eye watering.
Do you wear spectacles? Always have a spare pair in the car - in some EU states this essential (Germany) - its not a bad practice anyway.
Had a TomTom with french map last year -absolutely brillliant - the small tracks it took me down to access wine and fishing was brilliant - even if some of them caused a serious threat to suspension .
If you plan to go native as I prefer (and not fish where the first language is English ) learn the the names of the fish in French, learn a few basic phrases like What do you catch?, is the fishing good? and you'll find that the French are really helpful and love to talk, even if you don't understand a word!
