Apostrophes
The "correct" use of apostrophes is amply covered in any English book, and those of you who were paying attention in class or who read quality, edited text will have picked it up by now.
This page deals with the grey areas, the situations where apostrophes are wedged into or plucked from words with gay abandon.
Dates
If we're talking about the summer of 1970, we can say "1970's summer"; if we're describing fashion between 1970 and 1979, we say "1970s fashion" or even "1970s' fashion".
However, it is becoming common, almost acceptably so, to see a decade take an apostrophe: "Golfers of the 1970's". It's not clear why; we don't say someone is in their teen's. It's probably an example of widespread misunderstanding making illogical usage prevail. At present, the representatives of the view that pluralised dates should remain as plurals are making a comeback – but watch this apostrophe.
Letters and numbers
Does a cricketer score six 4's or six 4s? Did Sam get two As or two A's? Although the 4's and A's are plurals, not possessives, it is often clearer to use an apostrophe here, particularly with lower-case letters. This does not mean that PC's and VCR's are acceptable – abbreviations and acronyms are treated as normal words.
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