Kerouac...as for folks being tired and like a zombie after getting off a long flight...well...sometimes I'm a zombie and sometimes I'm not. I don't sleep on flights AT ALL...so by the time I've arrived into Paris or anywhere else, I'm TIRED.
And it can also depend on what's been going on in one's life BEFORE getting on the plane. I almost NEVER get on a flight relaxed. I've usually worked all day, cared for elderly parent(s), and done 100 other things before getting on the plane and am tired and exhausted when I leave home. I'm responsible for more lives than just my own.
I feel a lot more rested when I fly to Bangkok...17.5 hours non-stop, from Los Angeles, than I do when I fly from Los Angeles to Paris...which usually takes at least one change of planes and hours sitting in an aiport somewhere in the U.S.
So, the shuttle service is there for us zombies to use and I have absolutely no problem using it when I just don't feel like dealing with the RER. To each his own. Happy Travels!

Aggiegirl...If the shuttle is your mom's first choice, then I think she's trying to tell you something. I took a shuttle, in the spring, and had absolutely no problem at all with the company. You can pull up my thread, by typing in the SEARCH box, "Guenmai's Paris Apartment Rental Experience". I wrote about it there. Happy Travels!

I agree. To each his own. If you fly from the east coast most likely you'll be energetic getting off the plane and ready for the RER. Really there are others who have to travel from the other coast (or farther) and it is tiring so either a taxi or shuttle is welcome.

I appreciate all the commentary. I will let my mom make the final call. Someone asked about her mobility and that is not an issue. She is in excellent shape, just isn't able to sleep on the plane and is always exhausted upon arrival. I can't sleep on planes as well, but I get so charged up upon arrival that I'm ready to hit the streets.

You guys have no idea - try flying from Australia to Europe then you can start complaining about fatigue etc .

We took the RER from Luxembourg to CDG in June and it was a breeze, although very hot, so make sure you can take off a layer or two. St Michel and Luxembourg are both easy stops. And yes aggiegirl, Chatelet is a NIGHTMARE to be avoided at all costs!!

If you do catch the RER try to sit on the left hand side of the carriage and you will get a lovely glimpse of Sacre Couer!