I have Cav and Petacchi very close.
Gilbert will be up there, and should lead during/after the first week, but as has been said, we aren't even sure if he will commit to it as a goal. In order to win it he would have to fight on the flat sprints for the scraps, but I'm not sure he can even finish top15 with all the sprinters that will be here. Also I doubt his team is going to waste time on sneaky tactics which might help Gilbert get green, when their real goals are stages and GC.
Stages 8 and 9 only being 30 points is a big blow for Gilbert. If they were 45 I have him up with the other two.
Hushovd I have doing rather well, but I think I am overrating him, based on his Suisse efforts.
Not sure it's worth considering anyone else. No one is as fast as Cav, punchy as Gilbert, or resilient as Hushovd. Petacchi is fast and resilient if he is at his Giro level, but always a question mark over his commitment to seeing out the race.
If Cav wins I wouldn't be surprised for him not to wear green until the podium in Paris (all that matters!).