Like everyone, I got my carnets and used the Metro to get around. Great system.

Then, I discovered the carnet/pass is good on the buses as well.

Recommendation: unless you are in a hurry or need to make an appointment, take a bus instead of the Metro. You are above ground and getting a free driving tour as you go. Great sightseeing (what can you see underground?). There are many bus lines, and the bus stops have good labels and maps showing which buses stop there and their routes.

This goes for London, too.