Ara has posted a link to 5 Embarrassing Grammatical Mistakes by Martha Brockenbrough
In Martha's words. "it is a catastrophe of apostrophe to make a plural with an apostrophe-s." But there is this particular problem she mentions and which I faced only three days ago when I had to write to my Academic Dean:
"You can't easily write home about all the A's you got in English class if you don't stick the apostrophe in there. (It reads as though you're saying, "I got all As." As what? As if?)"
(You can work around this by putting the A in italics, but if you aren't careful when you change your typeface, you might lose it in the editing phase.)