Residency vs. Physical presence
Jackpot is confused. There are two ways to obtain the foreign earned income exclusion. One way is to be physically present in one or more foreign countries for at least 330 full days (that gives you slightly more time in the US than Jackpot indicates). Cut and dried.
But [b]that is not foreign residency[/b], which is the other way to obtain the exclusion. All you guys who are down here more or less full-time should read IRS Publication 54, which lays all this out. It's not particularly hard to understand, as IRS publications go. Furthermore if you are living outside of the US on April 15th you automatically get an extension to file. Can't remember right now if it's two months or four (Later: it is two months). All you need to do is write on your return, "Outside the US on April 15th" or some shit like that.
(Later) Keep in mind that an extension of time to [b]file[/b] is [b]not[/b] an extension of time to [b]pay[/b] so if you owe money, or think you might, you need to settle up by April 15th (note that the actual due date is the Monday following April 15th if April 15th falls on a Saturday or Sunday) or face interest and penalties. This can be done in a number of ways: with the extension form 4868 (or is it 4686???); via the vouchers for making estimated tax payments, or by mailing cash directly to George W Bush or any of his cronies (just kidding with that last one).
Oh yeah and filing for the FEIE does not require you to attach proof you were out of the country for 330 full days. You'd better [b]have[/b] proof if you get audited though. Here Jackpot is on the right track about the passport as proof [i]in the case of Argentina[/i]. However, bear in mind you can get the exclusion just as well by having been in countries such as Mexico which you can visit without a passport (at least under some circumstances).