I've had enough letters misdirected and returned to me, for reasons valid and ridiculous (twice returned from someone whose name and address were correct, and still lived at that very address - very strange), that I always put a return address on everything. Everything. Yes, even postcards. Even Postcrossing postcards. So it totally mystifies me when people don't write return addresses on their envelopes.
I got a letter today from a blog reader who wrote once before, and I wrote him back. And he wrote me again, and this second letter is what arrived today. His original letter is buried in a box somewhere, if I kept it - and he didn't put a return address on this new letter. It's a nice letter in a beautiful handmade envelope, and I'd really like to be able to respond properly. [Edit 8/25: thanks, he emailed me his address! All good.]
And yes, in case you're wondering - I DO use an address book, but no one goes into the address book until our exchange is well-established. Sooooooooooooo many people only write 1-5 letters and then go away forever that if I put them all in my beloved Edward Gorey address book, it would be full three times over. So you gotta get over that hurdle for a while before you make it in there. And even then, if you write your return address all nicely on the corner on the envelope, or inside, then I don't even need to open my address book.
And thus concludes the rant for the evening. Thanks for hearing (reading?) me out.
If you don't use a return address, and you DO want a letter back -- whyever not? Please do comment, I am genuinely curious.