Despite free Wi-Fi service near and in Metro and train stations, usage was low: Esme Vos writes that only 1,700 people tried the free Wi-Fi in Paris during the first three months of the trial. A large minority only used it once (probably tracked via their MAC address). When Parisians return from their month-long vacations, they'll find it's now 10 euros an hour to use the service that they weren't using in large numbers anyway.
I suggest you open your notebook at Chatelet station and count how many minutes you'll be able to use it before being "notebookjack'ed"...