There doesn't seem to be updated or current information on the various shuttle services available from Paris CDG to Paris (my hotel is in the 5th) on this board. I'm hoping those of you who have used the shuttle services available from CDG to Paris will share your experiences. Must these reservations be made in advance or can I simply pick it up at the airport? Is there a price savings to booking in advance? Some seem to be less expensive than others. I have been reading reports that a few of these companies are not reliable so I would really appreciate your comments about these various services - the good, the bad and the ugly. Please be specific and tell me which company you used and if you would recommend them (or not!) Merci!

I used Parishuttle.com last month and it was fine.

www.shuttle-inter.com was very good. It was 60€ for four of us.

I also had a good experience with Parishuttle.com last month.

You might check with your hotel. We stayed in a very small hotel and they had a shuttle service. It seemed high until we took the bus and then metro route. After the long flight it was just too much (physically). I would have paid the shuttle fee in a heart beat and will next time.

Don't use these guys. From my TR:

We had requested Golden Air shuttle the day before (recommend by Rick steves as “reliable”). They gave us a time after we told them what time our flight was. The driver was late. We called him twice, and he called our hotel once, but after 45 minutes of waiting, we asked the hotel clerk to call us a taxi. Their promises to be there in 5 minutes and then 1 minute were lies. I told them the last time, after a 30-second promise, that they had five minutes before we called a taxi. 8 minutes came and went. I asked to have a taxi called. The clerk told us that if we called a taxi we couldn’t us the shuttle because he would have pay the taxi. We agreed. He called the taxi. The shuttle shows up less than 2 minutes later. He was sent away and didn’t bother to apologize for the 50-minute delay. The shuttle would’ve cost us 34E. A taxi cost us about 42E.

Shuttles usually require advance reservations. It should be pointed out that there are two types of shuttles at two different price structures - shared ride and private.

The shared ride plans can be slow to depart the airport (as you wait for other passengers) and take a good amount of en route time if you are not the first to be dropped off. In general I do not recommend them finding the low cost alternatives more attractive if not a great deal faster.

The private shuttle services are very convenient and the personalized service probably worth what they charge which is very near the price of a taxi. There are companies about which I have only heard good reports:

http://www.paris-blue-airport-shuttle.fr/
http://www.shuttle-inter.com/
http://www.beeshuttle.com/

I like the convenience of taxis but if I feel the need to economize I'll take the RER B, AF bus, or Roissybus into Paris.

You have different ways to go to Paris.
First the RER, which is very convenient and cheap : 8,5 euro/pers.
But be carreful, use only the RER who goes directly to Paris (Gare du nord, chatelet..). Avoid some of them who stops before in suburbs city, depending of the hours you take it, it could be dangerous sometimes. (avoid Aulnay sous-bois, le Blanc mesnil..). To be sure choose a train with a lot of people inside.
The second way is to take a taxi. But it could be difficult to get one sometimes because there's too much people waiting for it.
So you have private shuttle service, but you have to book it first a few days ago. The price is more or less the same as a taxi. But your driver is waiting for you at the airport (no time to lose). The price is fixed, they accept until 8 people and you will pay the driver once you arrive at your hotel. (credit card accepted)
I recommand these one, which are cheap and efficient :
www.allonavette.fr (a private one, only you in the shuttle)
www.paris-blue-airport-shuttle.fr

I don't think you can get a shuttle on-site at CDG, that is usually a regulation and worked out in agreement with the taxi union, as then they would be in direct competition. There are some cities where you can just get them on-site without advance reservations, but others where you cannot, and I think CDG requires reservations in advance.