Recently, I was with a colleague who wanted to post some letters. We'd been out for an hour at lunchtime, and it wasn't until we'd arrived back at the office that we found a postbox - just 10 metres from the front entrance of our office. French letterboxes are bright yellow, and although they are far smaller than the traditional English red pillarbox, they should in theory still be very noticeable in the street. However, perhaps because of some similar effect to the luminous clothing theory I mentioned before, or perhaps because we simply don't post letters anymore, they seem to have become invisible. There could be a letterbox every 50 metres, or they may all have been removed from Paris overnight and I wouldn't notice either way.
Whilst La Poste is obviously still an ongoing concern as a financial institution (it provides banking services for people who would not be able to open an account in a standard high street bank), and as a delivery of parcels and other non-standard communication, how many people today take the time to write a letter by hand, address an envelope, lick a stamp, paste it on the envelope then put the envelope into a postbox? And if postboxes are now so infrequently used, will they begin to disappear, and if they do, will we notice? Close to my office again I recently saw a phone box being dug out of the ground, lifted onto a truck and taken away. If I hadn't witnessed the event, I would never have known that the phone box had existed.
I found a report produced by the Senate in France explaining the evolution of the service. It outlines how the actual postal and delivery service has been slowly declining, but also that it in fact only represents around 5% of the activity of La Poste.
To counter that report slightly, here's an interview with France's most famous postman, Olivier Besancenot.