Under the current laws, intent is irrelevant. If you meet certain criteria (net worth above $2 million, for most people) you pay tax. Our friends in Congress want to define people as meeting these criteria as having evil tax-avoidance motives. It ain't so, at the moment.

And of course NO ONE ever tells the Embassy official that the primary motive for renouncing citizenship is tax-driven. :-)

Seriously, though. I would say that at least half of the people I work with end up living in high income tax countries (Canada, various countries in Europe, Australia, New Zealand). They aren't leaving to cut their income tax bills. The tax-drive motivations are primarily (1) the craptastic paperwork and horrific penalties that Americans abroad face, and (2) the estate tax.