I have been a staff person on two different tours that followed the TdF (2004, 2005), and have seen the Tour in the Alps, Provence and in Paris. You learn a lot driving a van and shepherding lots of paying guests to and from the Tour stages! Feel free to e-mail me directly for specific questions and hints, but some general thoughts:
1. Mountain stages are, of course, the best for spectators, as on the flats all you'll see is the peloton blowing by for a few seconds. If you are in an area to see a flat stage, by far the best viewing is at the Depart (start) or the finish. I prefer the Depart, as you'll see the riders warming up, signing in, and otherwise milling about. You can also try to get autographs if you are into that.
2. For the mountain stages, it is possible to get a good spot without camping out the night(s) before. But, it takes effort and the use of your feet (either to walk or pedal a bike :-). I was on Alpe d'Huez the time-trial year (2004) and got there mid-morning, but still got a decent viewing spot (and that was the craziest and biggest crowd I've ever seen). Likewise, on the Galibier in 2005. The trick is to get there early enough to get to a good spot before the road is totally closed. They will close the mountain roads to cars usually 24 hours before the race comes through, but you can still get up under your own power up until maybe two hours before the race comes through (the caravan comes through about an hour before the riders). I'd HIGHLY suggest taking or renting a bike in order to get you into the areas where cars are banned.
3. As far as where to spend your time, it depends on when you are going, what else you want to see, and whether you are willing to put up with crowds. Again, the mountain stages are the best for overall viewing and "experience." It's a great vibe with all the crazy, international crowds up in the mountains. The addition of the cobbled stages in Belgium this year also add an interesting option. The finish on the Champs in Paris is great fun if you are still around. If you are going to check that out, stake your spot out early on the cobbled section leading up to the Arch d'Triomphe, maybe even paying a local restaurant a few extra Euros to let you hang out for the day. You could do a nice tour this year following the route by flying into Paris, taking the train to Lyon, renting a car there and viewing the Alpine stages, those in Provence, the Pyrenees, up into Bordeaux and then the finish in Paris. However, I'd suggest picking either the first half with the Belgian section and the Alps or the second half with the Pyrenees and the finish in Paris. Honestly, after a while it starts to look the same, even for a die-hard TdF fan and you'll start to get burned-out. For ideas on itineraries you could always scope out commercial tour groups and see what they are doing.
The "official" newspaper of the Tour, l'Equipe, publishes a schedule every day of when the Peloton will pass a given area/street/town. It's invaluable for planning. Make sure to pick one up every day. I think this info might be available on the Web ahead of time, but I can't recall where.
Lodging can be challenging to find in the more popular areas, since you are competing with the teams and all the TdF personnel, the organized groups, and other fans. Best to start booking NOW!
A note about photography: if you want to take good photos of the race, a film or digital SLR is a must. Point and shoot cameras generally have too much of a shutter lag to catch the action. See the below attachment for my favorite photo that I took during the 2005 Tour (Botero reaching the top of the Galibier).
Feel free to e-mail me directly with specific questions. briwasson A T verizon DOT net
