Re purchasing a Museum Card at CDG -- I found them at a tourist info place there, a small space like a newsstand with maps, etc. This was several years ago and I don't remember the exact location, but it was not difficult to find, even after the overnight flight from the U.S.

If you really like to see what is in the museums, the pass is well worth it. Bypassing lines is nice, but what I liked most was that we could spend a half day in a museum, then go back the next day for another half day. While some of the museums are easily seen in a day, certainly the Orsay and Louvre warrant more than a day, each, and I find it much more pleasant to take my time over several days, than to try and see everything in one visit. In fact, you can't see all of the Louvre in one day, as they close some of the galleries on certain days because of limited staffing.

We planned carefully to visit attractions on the pass during the term of the pass, and leave other attractions (such as the Marmottan, well worth a visit) for other days.

It was worth it just to skip the lines and to be able to make short visits to places you wouldn't bother going if you had to pay full price to get in. Bought just 1 adult pass and that allowed me to take along my 2 under-18 kids. Waltzed right by huge lines at Ste. Chappelle, d'Orsay, Louvre, etc. With only 3 short days in Paris, we didn't want to waste time in lines.

We bought the 3 day pass last year at the Arc de Triomphe. We were first timers and had just walked from the Eiffel Tower. I think we MAYBE broke even, and never used it to avoid a line, since the lines weren't too bad at the time. We probably rushed through some places, trying to fit more in. My DIL and son are going in a couple of weeks. She has been before and is weighing the merits of the card.

For us, it was definitely worth buying to avoid the long lines at the Louvre, d'Orsay, Ste. Chapelle and Versailles.

Robespierre, thanks for pointing out individual site costs. Hadn't thought of that, but realized Sainte Chapelle would also be on my list. If they have lines, then yes, worth it. DH absolutely doesn't do lines!