Thanks for the heads up Travlin.
Have heard about this before but spent some time researching at the IRS sight.
This is NOT a requirement reportable with TAXES. It's a stand alone reporting mandate made, as you correctly state, by June 30.
No extentions... all mandatory (didn't get into the penalties but can imagine!).
Any holdings (cash, coin, currency, securities, etc) over $10K in the aggregate (cumulative) is reportable.
Yearly reporting deadline: June 30th (Saturday). This Saturday for 2010 calendar year.
It does say there is an electronic filing system ... but also addresses (including physical for overnight packages) for reporting.
Important catch... google IRS foreign accounts reporting. DYDD - hoping I got it right and let me know if something I didn't catch.

“US Persons” are required to report to the IRS financial accounts they have out of the USA, and this includes precious metals. The report must be received at their Detroit office by June 30. I realize this doesn’t apply to most members and others already know. But this can be a surprise if you started a precious metals account in 2010 at places like BullionVault or GoldMoney. I learned about it from a thread here previously. I'll try to post a reminder earlier next year.
You'll find the details here. http://www.chrismartenson.com/forum/june-30-deadline-report-foreign-accounts-irs/59671
Travlin