There's a bit of a feud going on right now between stick-up-the-ass designers and tasteless ignorati about smart quotes. (That's when your quotes go left or right depending on whether you are opening a quote or closing them.) The discussion was stirred up by a website, Apostrophe Atrophy, which finds fault with signage that uses non-directional apostrophes, and seems to think that a huge design faux-pas was committed in each case. Certain font geeks, like John Gruber, seemed to agree. Then the backlash started, in the comments section of a page that initially presented non-directional apostrophes as an "unforgiveable graphic design gaffe".

I'm going to throw my hat in with the back-lashers here (as you may have guessed by the fact that I'm not using smart quotes anywhere in this post or site).

First of all, apostrophes are not quotes! They are completely different punctuation marks, which serve a different purpose. Telling someone to use "smart quotes" in place of a non-directional apostrophe is just plain ignorant. It's like telling them to replace their minus signs with em-dashes, or their zeroes with Os because the latter characters seems to be more typographically sophisticated. Guess what? It's not sophisticated, it's dumb.

By convention, apostrophes can be represented using non-directional marks, or using right-single-quote, at the discretion of the writer or typesetter. This is simply because in the early days of type you would use economize by reusing similar glyphs for different purposes. The use of single-quote for apostrophe owes itself to this glyph multi-purposing. That doesn't make it any more correct than using lowercase L for the number 1, which was also very common. (Old typewriters didn't even have a "1" key!)

Computers need to distinguish between Ls and 1s, so we're diligent about using different characters for them now. Computers don't care about opening-vs-closing quotes, however, so we're going to be arguing about this one for some time to come. Today, we consider both versions of apostrophe to be correct, and if a particular one is dictated, it is only because of a publication's style guide, or a particular font designer's intent, not any universal design or punctuation rule.

Esthetically speaking, directional quotes that resemble 6's and 9's also have a very crude serif feel to me. They look like fallbacks to the ancient typewriter fonts that put balls on the ends of their glyphs (such as American Typewriter Light). Why designers should feel that a design ethic that traces back to Underwood typewriters is superior to something from after, say, the Second World War is a mystery to me. When quotes must be directional, I usually prefer wedge-shaped marks. (In fairness, the non-directional apostrophe in many fonts is equally ill-conceived, being either a repurposed mathematical prime mark, or a crude rectangle that has no trace of type design whatsoever.)

Directional quotes enclose text (just like parentheses). Sometimes (often!) using a directional apostrophe is just plain bad typography, since it visually implies a closure where there is none. Example: The contraction ‘’tis’ is little used these days. Distinctive apostrophes (which usually means non-directional apostrophes) should always be used, in my opinion, to avoid typographic muddles like this.

Lastly, smart quotes look like crap on many viewing platforms. There are many reasons for this. The web is a low-resolution medium, and apostrophes and quotes occupy only a few pixels. Furthermore, the actual character codes and glyphs used vary widely, depending on whether something was pasted from Word, typed using HTML entities, referenced as Unicode, or something else. The compromises that get made in some cases to make smart quotes appear "smart" are truly awful. It often involves font- and character-set switching so that the quotes are rendered differently than the surrounding text, with faulty spacing and sizing. Reading the Wikipedia page on quotation marks on some browsers that have to jump through these hoops is enough to make you want to kill the inventor of smart quotes. Nothing looks dumber.