I'd like to present this today not as a chastisement of those who are doing it wrong but as enrichment for those who would like to do it right. If you are part of the ever-growing crowd who views the apostrophe as optional and spelling as a game of phonetic horseshoes, feel free to continue to ignore this. If, instead, you're interested in setting yourself further apart from said crowd, then read on.
The acute accent, in English most often found above an e in French loanwords like soufflé or café, is one of those nice little touches you can do that makes your writing look classy. At least, I'd like to think it makes you look classy. At the very least, I'm mildly impressed when I see someone bother to get their é's right in an informal setting like the Internet. As an added bonus, nobody will ever think you mean "I'm wearing a lame dress" when you say "I'm wearing a lamé dress."
It's not that hard to type, even though there's no é key on a standard American keyboard: on a Mac, type option+e followed by an e; on a PC it's a bit less natural, hold down the alt key and punch in 0233 on the number pad for é or 0201 for É. An apostrophe is not a substitute for an acute accent, and do take care not to hastily throw some other kind of mark over the letter like ē or è or ë.
And now that you know how to make an é, let's talk about when. When you've got an "e" making an "ay" sound at the end of a word, it's a fair bet that there ought to be an acute accent there helping it out*. When you've got two e's at the end, as in fiancée** or Renée, the accent always goes over the first e. Most spell-checkers will flag your word if you've forgotten an accent, though if the world sans accents is also another word (as in lame, resume, expose, etc.) it'll slip by. Another easy method to look up the proper accented spelling is to do a Wikipedia search for the word without accents and see if you get redirected to an accented version.
Alright, I'm done lecturing at you now. Class dismissed!
* One notable exception is the not-strictly-proper use of é in Anglicizing Spanish loanwords like mole and mate by changing them to "molé" and "maté." Doing so looks perfectly natural to someone like me who took French in high school but probably drives the Hispanophones batty.
** You can earn bonus points by remembering that if you are engaged to a man, then he is your fiancé -- one e -- but if you are engaged to a woman, she is your fiancée -- two e's. Same rules apply to divorcé/divorcée. When you use the wrong one, I like to assume that you used the right one and I merely did not know your sexual orientation as well as I thought I did.
