I am amazed at the lack of faith in Cavendish in this thread. I can not understand how some people write him off so easily (the same that wrote him off in 2010 and 2011) after being proven wrong so many times by him. It must be wishful thinking.
Cavendish loosing a couple a stage is one thing but suggesting that he won't won a stage at the TDF like some suggested is a bold statement to say the least. It's not like he is getting any slower or anything :
2010 prior to the Tour - 3 victories (Catalunya stage, Romandie stage, California stage) = 5 TDF stages
2011 prior to the Tour - 4 victories (Oman stage, Schelderprijs, Giro stage X2 (+TTT)) = 5 TDF stages + green jersey
2012 prior to the Tour - 8 victories (Qatar stage X2, KBK, Tirreno stage, Giro stage X3, ZLM Tour GC) = ?
Of the riders in the poll, Farrar has shown nothing all year and does not have the same motivation as last year, Goss has won a crash marred sprint in the Giro and that's basically it, plus he is more an uphill style of sprinter, Renshaw is overrated, has no train and only a win so far this year (Turkey stage).
It would be unlikely that they win a flat bunch sprint at the TDF this year (Goss could take a stage like Seraing though).
Sagan and Kittel are discovering the Tour and are going head to head with Cavendish for the first time so it is impossible to judge them yet.
Greipel is going to challenge Cavendish but remember that his victory against Cavendish last year came after a massive fail of the HTC train and Cavendish had to go way too early to catch Oss (circumstances unlikely to repeat themselves).
Petacchi though not in the poll deserved to be mentioned as he always manage to take a couple of stage of Cavendish no matter what his form appears to be before the Tour/Giro.
Freire can never be counted out and Rojas was very strong last year but it is hard to see them win a bunch sprint (rather stages like Annonay/Porrentruy).
I think that is about it for his competition.
Now let’s look at his opportunity for winning stages :
Stages where he will compete : Tournai, Boulogne-sur-mer, Rouen, Saint-Quentin, Metz, Le Cap d'Agde, Pau, Brive, Paris
Stages where he could compete (aka not the favorite but not a huge upset if he won there) if ridden with favorable circumstances : Seraing (last climb will probably be too tough), Porrentruy (the climbs are unlikely to be raced hard + are short so if he starts the climbs at the front of the peloton he probably won't have time to get dropped from the group), Annonay (the climbs won't have any impact because too far from the finish), Foix (breakaway stage so the climbs will be ridden slowly + far from the finish, if for some reason the breakaway does not suceed Cavendish could clean up). They might look like a stretch but remember 1) that Cavendish always finds his climbing legs for the Tour 2) he has supposedly lost 4kgs 3) his Aubenas stage win in 2009.
How many he wins will be determined by when/if he pulls out, how committed to him Sky will be, how many crashes he is involved in (or rather triggered

), if he is able to break his "course" of losing the first bunch sprint of a GT, and how Kittel/Sagan will fare. Barring illness or injury, I'd say he will win 6 but more conservatively I would say 3-5 is the most probable outcome with Greipel/Kittel/Sagan/Petacchi winning the left-overs bunch sprints and Freire/Rojas/Sagan/Goss winning the tougher sprint stages.