I know other blogs have already covered this. I found 3 very quickly when I did a Google search. However, I am going to give this a shot anyway. Glen Whitman says it very well on his blog. Machine operated hand dryers do not do a good job of drying your hands, they aren't hygienic, and they don't save the environment. They are easier for establishments to maintain though because they don't need to be restocked and they don't generate more trash so they require less staffing of the bathrooms. It's an old topic. Another blog, "The Volokh Conspiracy" also references Glen's rant and adds a few more lines on the topic. Another blog touches on the subject but only to say that the air dryers are more efficient than paper towels.
None of those though mention a problem I've encountered with the machines. Those loud hot air things scare my 2 year old. We have had to leave several public restrooms with wet hands because she was scared of the noise that these things make. We are over that phase now thankfully, and have started to actually use the machines but they don't dry your hands (as Glen Whitman pointed out) so my dear daughter still ends up wiping her hands on her clothes or on mine. It is annoying enough to deal with restrooms with no diaper decks or a place to put your purse, but to have to deal with a kid with slippery wet hands is really a hassle too.