About the Paris Museum Pass

Yes, as many entrances at as many museums as you want during the period of validity.

Yes, fellow Olympian, you can use it as often as you want within the period it covers for any sights it covers. But there's no 3-day pass, only 2, 4, or 6 days.

You can buy it any time, but don't fill in the starting date until the first time you use it. Then you have however many days you bought to zip around from museum to museum. As I recall, it covers full days, not 24-hour periods. So start in the morning. And remember that some of the big ones are closed on Mondays or Tuesdays, but open certain evenings. So be strategic with your timing.

One thing I like about the pass is letting you visit places where you might not otherwise invest in the admission fee -- "minor" museums or those where you want to see just one or two things. Or just use the bathroom.

Yes, I visited the Pompidou twice. As others point out, it's great for popping in for a second peek, to use the restroom or visiting a museum or site you might not have otherwise. I found it a good value.

Many thanks for all the replies, certainly answered my question.