[lavela]

Maybe I am missing something, but I haven't seen a solution to the noise problem of air traffic (especially anything rotor based).

Might not be an issue for long distance connection in sparsely populated countries like the United States, but I don't see it replacing trains in Europe until this is solved.

[bobthepanda]

There is also the fairly obvious problem of safe operations in urban areas.

Rooftop helicopters were banned from Manhattan’s office buildings after a helicopter tipped over and decapitated waiting passengers, and then the blade fell to the street level where it killed another person.

[xnorswap]

Flying no matter how diminutive always has the issue of Newton's third law. This requires having large empty landing zones to be safe, or you risk having people land on you, which would hurt no matter how slowly they're coming in.