We were in Paris the third week of June, and we were happy to have the PMP. We needed a timed reservation for the Louvre and the Orangerie, but we were able to enter the d'Orsay, Rodin, Les Invalides, and Cluny museums with no problem without committing to a time ahead of time. Traveling with kids, we appreciated the flexibility of not having to have as many timed tickets reserved in advance. (We did go to the d'Orsay first thing, so I can't speak to how the lines would have been later in the day.)
One note of caution - make your timed reservation for the Louvre as soon as possible. The PMP time slots ran out more quickly than the regular slots. I would suspect this would also be an issue for Versailles.
Another note -- we ran into trouble at Les Invalides because we had to wait in a very long line to get free tickets for our children, who did not have PMPs since they are free at most places. It ended up faster to go on-line while we were in line and book free tickets for them on the museum's website. If they hadn't been with us, my husband and I would have been able to walk right in with our PMPs.
One final note -- the only place we ran into trouble with the PMP was trying to get into the Arc de Triomphe. We arrived at mid-day, and the line for visitors with passes was so very long. I suspect it would have been well over an hour to get in. We ended up skipping it. The line to enter with a purchased ticket was virtually non-existent.