Giving up your U.S. passport will now come at a very high price. A new law signed by President Bush on June 17, 2008 (H.R. 6081) will subject certain people who decide to expatriate or turn in their green cards to an immediate exit tax.
The new rules apply to certain individuals who expatriate as of June 9, 2008 and
Certain exceptions apply to individuals born with dual citizenship and those who relinquish US citizenship prior to age 18 1/2 (provided certain requirements are met).
The impact is fairly significant for affected expatriates and is far worse than the "old" rules. Withers Worldwide has put together a pretty comprehensive summary of the "new" rules entitled "Exit Tax for U.S. Expatriates to Become Law”, so I won't re-create the wheel here.
Source: Maxim Global Wealth Advisors, By David Colvin, CPA, CFP - 2008