[freshyill]

I think two spaces after a period is more of a typewriter bad habit than American thing. Back when you had a single monospace typeface, I think it just made things more legible. People who learned it then passed it on to generations who never used a typewriter.

[xyclos]

anecdotal, but when I was in grade school (in the US) I was taught that it was a MLA rule to use two spaces after a period. I had teachers that deducted points from a paper if the extra spaces were missing.