When you send e-mails full of misspellings and errant apostrophes, people judge you. And by people, I mean me.
It’s better than fashionable: it’s useful.
Wildly original and excessively heterodox language could land you in the soup.
You slip into a suit for an interview, and you dress your language up too. You can wear what you like linguistically or sartorially when you’re at home or with friends, but most people accept the need to smarten up under some circumstances. It’s only considerate. … There’s no right language or wrong language any more than there are right or wrong clothes. Context, convention, and circumstance are all.
(More on Stephen Fry.)