From TPM Reader JG ...
I can't speak for the quality of Mr. Saverin's legal advice going into the renounciation process, but as a consular officer with the Dept. of State who's done denounciation of citizenship overseas, I can assure you that we're under guidance to go over in detail with the applicant the potential consequences renounciation for purposes of evading taxes, and the visa ineligibility they may face. By the time he gets to the session with the officer, he can't claim ignorance. We also also gave them two weeks to think it over. We don't like having to deal with folks coming back saying "just kidding."
The key remember is whether the United States government decides that he did it for tax reasons, which seems pretty obvious. And that's why his lawyer is now insisting that dodging the capital gains tax on the Facebook IPO had nothing to do with Saverin renouncing his US citizenship.
One TPM Reader says the the particular US law has never been enforced. But it's also true that renunciations of US citizenship for tax purposes has grown a lot in recent years. And I suspect there are pretty few examples where the bill in question was for $67 million.
Late Update: Here's the form you need to fill out to renounce your US citizenship. Note item #10.