Well, you've heard today from those who swear that each and every letter you read in a magazine has come directly from a reader (albeit one more than likely serving time on the orders of the state). Now, let's take a look at the other, more believable side. After the jump, voluminous evidence that certain publications—some of which you even read—play fast and loose with their letter section.

When I interned at Stuff, it was common practice for interns to write a large portion of the letters to the editor. We rarely had enough letters from people who weren't fucking insane prison inmates to fill the space, so somebody had to do it. This was the case at another mag I worked at, as well (not going to name names on that one though). I always assumed fake letters to the editor were commonplace. And apparently I was right.
I spent a couple of years editing the letters column of a major magazine, and let me tell you...it wasn't easy filling the space with pity and cogent missives. Let's face it: people are idiots.
I was in San Francisco in the summer of 2003, minding my own business. Only I hadn't told my old flame I was on break from from New York, because I wanted to avoid falling into the habit of sleeping with him again. He was on a plane returning to SF from Italy when he thumbed through the current issue of Blender, where my friend was an editor at the time. When his plane landed, he emailed me, "why does Blender think you are in San Francisco?" I made a panicked call to my friend at Blender. She said, oh, I had to make up a bunch of letters to the editor, and I signed your name + San Francisco to one of them." I ran out to get a copy of Blender. The question in my ersatz letter to the editor was something like "is there any truth to the rumors about an orgy with Margaret Trudeau and the Rolling Stones?" To dodge admitting that I was in fact in San Francisco, I replied to old flame's query with "I think the real question is, why does Blender think I don't know the nitty gritty about all the Stones' purported orgies? And the answer is: makes all that shit up." He totally accepted that answer, and didn't find out I was in SF for several more weeks. Most, if not all, of the letters to the editor at Blender were fake the whole time my friend was an editor, but often signed with real names of 's friends, and like, their hometown or someplace they had vacationed recently, so all the letters wouldn't look like they came from New York.
I know this to be the case at 'organic style'...as soon as i read this entry, it rang a bell, someone i know who used to work as a editorial asst there mentioned not just that letters were handed to her, but that they actually wrote them themselves... often.... like every month... so there you go after...after she told me that 2-3 years ago, I made the generalization that this is prob standard.
I used to work at Redbook, and the assistants on staff regularly made up letters and attributed them to friends and family. Later one assistant made the huge mistake of asking her intern to invent a letter. The intern later reported this as one of her internship "duties" to the journalism chair of her school. The professor wrote a letter to the editor condemning this "unethical" practice (dude's obviously never worked at a magazine; they're all hotbeds of unethical practices), and of course the assistant got fired to save face.
The Observer makes them up all the time—I've done it myself. Plus, one editor in particular bars the publication of letters criticizing his pet authors. However, the NYO letters column is so dull, nobody cares. [Ed Note.: One of us used to have an office a few feet from the person who handled the fact-checking of that paper's letters, so uh, grain of salt on this one.]
I used to write the letters describing erotic adventures in Blueboy Magazine. Seriously. $300 per month. Ironically, most of the experiences I wrote about were true. [Note: Some of us had never heard of this publication but were informed that it does, in fact, exist, and is exactly what you think it is. -Ed.]
If you want to see some fantastical fake letters, check out the Ask section on the first page in Parade magazine. If they are real, may god strike me down because I cannot think of a single person who gives a shit about any question I've ever read since I learned to read.