I did some checking into this question. It seems that most style books (Chicago for one) advise dropping the apostrophe, however, the New York Times uses it consistently still for these situations. I know that in older publications I saw "70's" quite a bit, etc.

Seems to be something which is changing fairly recently.

It is, of course, true that using an apostrophe to form the plural of an ordinary word will make you look like a doofus.