I took Roissybus to CDG on Christmas morning. I bought my ticket with 9.10€ in change from a ticket machine in the metro. It left on time and, with heavy rain and light but not non-existent traffic, took about 45 minutes to Terminal 2A--more than the 20 minutes the driver had predicted but not bad. I probably wouldn't take it on a normal morning, however. It would be pretty unpleasant if packed--there's really not enough luggage storage for the number of seats.