От 288466 (3,761 – 1·6·36) 25.03.2009 (Обновление 3.0.9)
If you mail (or give) the copy to someone else, if it was sent by an NPC and has your name in the text, when the person you gave it to reads it, it will have their name instead lol.
От 493392 (10,110 – 3·13·68) 21.03.2010 (Обновление 3.3.2)
I got mine on the AH for 100 gold.
It reads "Open Immediately"

 

От PalominoMule (772 – 8·13) 22.03.2010 (Обновление 3.3.2)
My sympathy goes out to those who dared to indulge their curiosity and hope people would at least put a bit of effort into the stuff they were selling, particularly given the low cost of investment.
Still, the fact that we indulge our curiosity says something about the worth of this as a means of communication. For those who like finding new and interesting ways to "play" WoW, producing more creative pieces and selling them for a more reasonable price might be a worthwhile form of expression.
It's also a bit challenging. What nobody has thus far noted is that in-game mail is restricted to 500 characters. Also, since there's no way to label plain letters, letting people know that you're not just posting 10 of the same letters on the AH is tricky. The only way I've identified to differentiate between different letters is to change the price. For instance, I might sell the first piece of a story for 10s01c, and the second piece for 10s02c.

 

От Raithon (2,085 – 3·25) 23.11.2009 (Обновление 3.2.2)
Hm...
This should be interesting.
*Spends 4 gold*
...
*Opens letter*
"Hello!
Please give a warm welcome to your new cool penguin pal!
I'm so happy you could give this sassy little spheniscidae a home.
--Breanni"
...
FML.

 

От Bsmx93 (13,872 – 3·30·107) 12.09.2010 (Обновление 3.3.5)
Blizzard's warden scans these letters.
So if you're planning on sending a friend a CD key or Game Key through the mail (or writing it on one of these letters then sending it in as a wrapped gift) expect a temporary ban.