At least as as I was taught in the US, North America is a continent, while Central America is a geographic region, as well as a historical, political group. Mexico is not part of that. http://www.worldatlas.com/webimage/countrys/camerica.htm

I personally never use the comma after the "eg" -- also do not use periods as you notice. To me, commas should only be used where necessary for clarity, or to signal a natural pause in the text (ie where you would pause if reading or speaking out loud).

Perhaps, but if so, I have not often seen it used.

>>Because the sports media aren't exactly known for high intellect.

I am not very comfortable calling myself "American" but, at least in my experience, most other residents of the Americas use the term only for residents of, or citizens of, the USA.

As noted, most others refer to themselves as Canadians, Mexicans, Brazilians, etc, or, sometimes as Central Americans, South Americans or Latin Americans.

In most cases, the "eight inches" refers to a (singular) measurement, not eight individual inches. So I agree, there are twelve inches in a foot, but a foot is 12 inches in length.

Off the main topic, but I agree with the UK idea of group nouns, although I get plenty of flak about that here in the US. Although we DO usually use the UK form for sports teams -- often because the names themselves are plural (eg Yankees, Broncos, etc), but even when not (eg Utah Jazz), we usually treat it as plural.

I would say that the "had always wanted to be..." form would only be proper if she no longer wants to be an author -- perhaps because she no longer enjoys it, or, of course, if the person no longer lives.

As others have stated, in spoken form, this is just a minor variation on "would've" etc. Unfortunately, it seems that too many people fail to recognize that that is not "would of" so they write it that way.

In informal use, or when reflecting the conversational form, I tend to write it "woulda" which is closer to what I hear spoken.

Generally, especially in the US, periods are not used in abbreviations -- especially commonly used ones (eg, ie, am, pm, etc) and also not in US or USA.

I do think foreign words and abbreviations SHOULD BE italicized, but that seems to be on the way out -- in part because it is a pain in the arse to do with most word processors. I do italicize them in formal writing, but not in everyday use.

This is an example of what is really an idiomatic expression, one which is not at all dependent on one's belief in a deity. But its basis is, of course, the traditional Christian God concept, in which, as mentioned above, God's knowing is in the present tense.

If one were to use a similar construction with non-supernatural beings, one probably would use either past or present tense, depending on whether or not they still know.

The "God only knows" expression is rather trite and overused, so it might make better prose to construct it in past, rather than present tense, just to be less so.