I am an American living in Prague and will be among those to give up their citizenship. The new FBAR requirements and the recently pushed through changes that require foreign banks to report are really a huge burden. It is a significant legal risk to be an American overseas. The fines are insane for failiure to report, even if you owe no taxes! You can easilly land yourself with a $20 000 - $80 000 fine for having a hundred bucks in the bank and no income. Indeed, it's not just double taxation, it's tripple taxation, because I have to have a special bank acount that is for Americans, and the fees for the "American expat" bank account are much higher than the ones for a normal bank account.
But I think that it is wrong to present this as a taxation issue. I would be fine with paying a percentage of my income in taxes. There are some benefits to being a US citizen, like that the army will rescue you if there is a civil war ;). But the fear uncertainty and doubt that surrounds these new regulations makes it nerve racking to be a citizen. Every expat I know here has nightmares about an audit comming and having all of their assets seized. And it has happened to some of them too! And that legal risk is no longer a form of taxation, because taxes are percentual (the more you earn the more you pay), but when you end up having to pay a fine that is higher than your net worth, that's just robbery.
We used to be a free nation, but thanks to austerity the 'r' had to be removed.