One Space Or Two Spaces?

When I began writing technical documentation and courseware for Guru Labs, I asked a question during training about whether we should be putting two spaces after a period, colon, question mark and exclamation point, or one. The answer shocked me, as I was hoping for the standard answer as a means of teaching the rest of my colleagues. The answer was ONE space, not two. Then, I listened to the argument.

Toponce, Aaron. Aaron Toponce (2008). Articles>Writing>Style Guides>Grammar