It can be a huge hassle for normal US citizens living outside the US. Most banks won't deal with them because of the risks involved. As a US citizen abroad, just getting a regular bank account can be next to impossible.

I live in Singapore and when I was signing up for a stock trading account I asked what would have happened if I had to answer yes in the box that asked if I was liable to pay income tax in the US. The answer was plain: "you wouldn't be allowed to have an account with us".