I thought about that very issue long and hard before choosing the P11 as my pocket pistol. It appears that if the pistol is dropped from a few feet high, with the muzzle pointed EXACTLY straight down, it MIGHT discharge. But that is true with a lot of other pistols as well. Also, while it might be very disconcerting if it were to happen, the shot would be straight down into the floor, ground, etc. I finally decided that the benefits of carrying it with one in the chamber outweighed the risks. I carry it daily in my pocket with a round in chamber.
BTW, I really like my P11. Zero malfunctions so far with about 150 rounds. The trigger sucks of course but that very long trigger pull makes it hard to accidentally pull the trigger. The hammer is well protected, like Feanaro points out, and not likely to be hit by or snag on anything . I personally feel very safe with this pistol.
Just my $0.02.