The Verge, on Microsoft Word now flagging two spaces after a period:

The software giant has started to update Microsoft Word to highlight two spaces after a period (a full stop for you Brits) as an error, and to offer a correction to one space. Microsoft recently started testing this change with the desktop version of Word, offering suggestions through the Editor capabilities of the app.

Daring Fireball’s John Gruber, delightfully pedantic on the issue:

The two-spaces thing has been a “debate” only in the way that wondering if the earth is round, or if man landed on the moon, or if you should smash up a couple of cherries and orange wedges while mixing an Old Fashioned, have ever been debates. One side has all the experts in agreement; the other side is wrong. Go look at a few professionally-typeset books — every single sentence on every page in every book has one space after the period.