My wife and I purchased the Paris Museum Pass; it is a good deal cost wise and does avoid having to purchase tickets at each museum, so would definitely purchase again. However, in many cases do not expect to "skip the line" for getting in. You are only skipping the ticket purchase line, not the entry line.
We saw both Americans and Europeans getting upset because the Museum Pass holders had to stand in long lines to get in - we found the pass holder lines to occasionally be much longer than the ticket purchase lines; in the case of the Orangerie museum, people got in faster buying a ticket there as they went from the ticket window directly into the museum. The entry lines for the pass holders at the Orsay, Orangerie, and Versailles were very long and everyone and whatever they were carrying went through metal detectors and package x-ray so this meant something of a wait. Seemed like most visitors had some sort or pass or other. In the case or Versailles, everyone queued up in the same very long entry line, whether you had a pass or ticket.
This was very different from the Firenze Card experience in Florence, where card holders are given priority entry before ticket holders and Firenze pass holders were less common.
Like everywhere else in Europe, best to get there early as possible. Good travelling.