In reply to GrahamD:
Most of the traffic will head to the centre of Paris to watch them go round the loop.
As long as you stay East of Evry, you probably won't notice anything unusual, however, even if you went the other way around paris (via Versaille) you would probably only see lots of folks standing on the bridge over the main road where the course crosses.
It won't be like the UK - the french see the tour pretty regularly so you don't get every cyclist in teh country turning up to watch every stage.
It is also very unlikely to use any major roads.