I wish you luck with your connection. I am looking at the same thing for an upcoming trip and have decided I do not feel comfortable with a connection time of less than two hours at CDG. I have had the same experiences as some of others of having to take a bus from out on the landing field to to terminal. Depending where you are sitting on the plane it can really take quite a while to deplane and get to the terminal. And while I agree that often times flights from the US land earlier than scheudled, I have also landed later. And finially, the last time I landed at CDG Terminal 2, the bus-shuttle thing (looks like a bus but you all stand up) deposited everyone from the plane in the same place and we were forced to go through passport control. I was staying in Paris that time, but I don't recall seeing an option for people who where transferring to skip it.

I think what you can take from this thread is that there are a variety of experiences and no guarantees. Since there are many flights to LHR you will most likely get one if you miss the once you are scheduled on, but it will be the next flight with available seats, not necessarily the next flight. You might end up spending quite a few hours at CDG waiting.