Thought I would share my experience this past week using the Paris museum pass. I was on the fence about doing it because I was worried about lines, especially at the Louvre and Versailles. I traveled with my 13 yo daughter and we arrived last Wednesday (5/22) and returned home yesterday (5/27). I ended up buying the 4 day pass for 62 euros as this was her first time in Paris and we were going to do a lot of sightseeing. In the end, I highly recommend the pass, we saved so much time by skipping lines. We ended up going to: the Louvre, the Orangerie, Musee de l'Armee, the Musee d'Orsay, the Conciergerie and Ste. Chapelle, the Arc de Triomphe. & Versailles. I added up all the individual entry fees (combo tickets for Ste. Chappelle and the Concergerie) and I would've spent 87 euros, so we did save money, but we also saved a lot of time. Here is how it worked at the various places:
Louvre: Museum passholders use the pyramid entrance with those that have timed tickets. We initially went to the Carrousel entrance, but were redirected to the pyramid entrance. Absolutely no wait and we went straight through security. There was a very lengthy line to buy tickets. My pass was scanned as we entered the Denon wing. This saved so much time.
Musee d'Orsay: We also entered this museum along with those that prepurchased tickets. No line for us and we walked straight in. There was a decent sized line to buy tickets.
Musee de l'Orangerie: There are 2 separate lines, one for museum passholders and those with tickets and the other for those who need tickets. The line for buying tickets was definitely longer than the other one, but neither was really long.
Arc de Triomphe: This was one that I had read that I would need to stop to get a ticket for my daughter. There was a pretty lengthy line to buy tickets. We went ahead and walked up to where they checked for tickets and they let us right in. Lots of time saved here too.
Concergerie & Ste. Chappelle: We had to wait in the main security lines (neither were very long), but Ste. Chapelle had a good sized line to buy tickets that we skipped. The concergerie didn't have any lines to buy tickets when we went.
Musee de l'Armee: We did have to get a ticket for my daughter, but there weren't any lines.
Versailles: We arrived at the chateau around 12pm on Friday. We didn't even try going to the chateau first (the lines were pretty crazy as others have described) so I can't comment on if we would've been able to skip those lines. The line to get through perimeter security, however, was very short. We opted to do the gardens first (we did have to pay an additional 8 or 9 euros each as it was a musical gardens day). We bought those tickets at the gardens and there weren't any lines. We did the gardens until around 4 pm when we went to the chateau where we just walked right in.
Anyway, I highly recommend buying the museum pass if you plan on going to more than a couple of sights. It really is a time saver.