Ten typographic mistakes everyone makes

Grammar nazis are so last century. Welcome, friends, to the brave new world of the typography nazi. Below are ten mistakes that everyone makes, an explanation of why each is wrong, and details on how to fix them. At least, you'll see how to fix them on the Mac; under Windows, you'll need to dig through tables of Alt characters. Have fun. (If you decide it's time to be more accurate with your type on the Mac, get PopChar.)

Such typographic faux pas are not as potentially dangerous as grammatical fuckups – there's little chance that using a period instead of an interpunct will obscure or confuse your meaning – but they are nevertheless wrong, at least for the time being. The large-type heading for each section contains an example of a typographic mistake; if you can see what's wrong in each one before reading the explanation below, give yourself a pat on the back. Then examine your life priorities.

One last disclaimer before we get started: by ‘mistakes everyone makes’, I include my lazy-assed self and exclude you if you're a professional typographer. Or just someone who care about the little things in this amoral pit of a world…

"What's wrong?"
OK, an easy one to start. Yup, those aren't proper quote marks; they should be ‘sixty-six and ninety-nine’ quotes. The mistake happens because typewriters, pushed for space, decided to have only one neutral quote on the keyboard, not dedicated opening and closing quotes, and the convention stuck.
THE FIX: alt-[ and alt-shift-[ for double quotes; alt-] and alt-shift-] for singles.

New in iWork ‘08!
Of course, now we have word processors that do smart quotes for us automatically, everything's cushty, right? Wrong. If you type the above sentence in Word or any other modern app, it will think that because you type the first ‘apostrophe’ in a sentence, you want an opening, ‘six-style’ single quote. Instead you actually want a ‘nine-style’, closing apostrophe, so you have to enter it manually – or type two and go back and delete the first – so that the sentence reads New in iWork ’08!
THE FIX: As above.

I am 5' 10" tall
So those 'straight' quotes aren't for proper quotes, but they represent feet and inches, right? Wrong. They're not actually for anything. Feet and inches should be represented by primes, which look a bit like straight quotes tilted slightly to the right. If your browser supports the characters, the above statement should read: I am 5′ 10″ tall.
THE FIX: Sorry, but this is a bugger to fix. If you're in InDesign or QuarkXPress, use the glyphs palette. Otherwise, OS X's Character Palette – check the International pane of System Preferences – is your only salvation.

10.5″ x 9.4″ x 4.5″
You fix one problem, and another one just bloody well comes along. So, hurrah for getting the primes right, but using a lowercase X for the ‘by’ character is another lazy I-can-see-it-on-the-keyboard-so-I’ll-just-type-it thing. Correctly rendered, the above measurement should be 10.5″ × 9.4″ × 4.5″, not 10.5″ x 9.4″ x 4.5″.
THE FIX: Again, a tricky one. You'll need to break out the character palettes.

14º and overcast
This is a really subtle one, but that degrees symbol you see up there isn't a degrees symbol at all. It's actually an O ordinal, used, inter al, in Italian, Portuguese and Spanish to denote masculine gender.
THE FIX: alt-0 gives you the ordinal, while alt-shift-8 is a true degrees symbol; alt-K is a ring above accent. [thanks, silverpie!]

Some - indeed most - use hyphens incorrectly
A hyphen – the kind of short dash you see above – should really only be used when linking words such as ready-made. It shouldn't even be used mathematically to represent a minus, as there's a dedicated character for that, too [thanks, Dash Nazi!]. Most other uses mandate an en dash – as here, for example – or when planning meetings from 1–2. Changing fashions mean the the long dash—this one, called an em dash—is rarely seen, but where it is, it's usual to render it without the spaces on either side or with special hairline spaces instead.
THE FIX: alt-hyphen for an en dash, alt-shift-hyphen for the em.

Only £17.99!
Again, laziness and the democratisation of typesetting mean that we've lost the use of the correct interpunct in prices. £17.99 should be correctly rendered £17·99. After decimalisation in 1971, a period was only supposed to be used if technical limitations meant that a middle dot couldn't be printed.
THE FIX: shift-alt-9 types an interpunct [thanks, Nic!]

Nobody cares...
Quite probably. But what you see above is just three periods, not a true ellipsis. Want a proper ellipsis? OK then… (In this font, three periods looks like this, much more tightly packed...)
THE FIX: alt-; types a proper ellipsis.

These (honest!) are brackets
No, those are parentheses. Brackets [like these ones] are used to add in information missing from a sentence you shouldn't change – such as a direct quote – or to add information outside the voice of the original text. And don't think you're smart using angle brackets to replace quotation marks when writing French; <en français> is horribly wrong, and you should instead use proper guillemets if you want to write «en français».
THE FIX: Just be aware of the difference, and don't call parentheses brackets! [Note that Lise makes a very good case for me being wrong in the comments, but I'm not so sure. More research is needed...]

3 1/2″ and 5 1/4″ disks are obsolete
Though complex fractions have to be created individually, most mainstream fonts have the characters for a quarter, a half and three quarters. 3½″ and 5¼″ not only look better and are more accurate than the use of the forward slash, but they're clearer too. 3 1/2 looks like ‘three and one or two’, and you obviously need the space in there otherwise it becomes 31/2. In this age of decimalisation, 3.5″ or 5.25″ are, of course, alternatives, but there are some uses where a proper fraction is more sympathetic to the source or context than a forced decimal.
THE FIX: You're going to need your character palettes again. You didn't just tidy them away after the last time, did you?

Well, how did you score? Do you have your own typographic bugbears? Or am I just an insufferable busybody who will hasten myself to an early grave, getting my panties in a bunch about stuff that doesn't matter a damn? That's what the comment box is for…