Dunno.
Saying ".__" is always wrong strikes me as a bit too dogmatic. Like others, I was taught in typing class that two spaces go after a period that ends a sentence.
A lot of text that's published is fully justified or uses [link|http://www2.ncsu.edu:8010/ncsu/grammar/Typo3.html|compensatory spacing] - the spacing on the line is adjusted to minimize the jagged right edge. An example is provided in the sample pages in the book Jake pointed out on Amazon. Saying there's a hard-and-fast rule that one space goes after a period seems a bit simplistic to me.
As the link says, with compensatory spacing, it's most common to use one space. But it also says that the proper choice can depend on the font used.
So, I dunno.
Cheers,
Scott.
