This issue periodically makes the rounds in expatriate communities, and I think panicked blog posts outnumber actual enforcement actions by about 10,000 to 1. Anecdotally, most Americans living abroad are probably non-compliant on this one. They're not going to suddenly decide to break the kneecaps of a couple million people, for the same reason that they don't audit every $50k per year small business' office expenses every single year. They'd end up hated and not meaningfully boost revenue.

All bets are off if you have signatory authority on a $30 million dollar account in the Caymans and have forgotten to report interest for the last 10 years running.

P.S. Orthogonal to the disclosure of accounts issue but worth mentioning since folks often commingle them: If you're an American living abroad, you should file your taxes every year whether you think you need to or not. Same for Americans in the US, by the way. The statute of limitations on unfiled taxes is essentially infinite, but the window to audit a return is only six years, so if you just file a 1040 with a zero on it every year and 20 years from now the IRS decides to get frisky, you're covered for all but the last 6 years automatically.