First, allow me to tell you that I am extraordinarily impressed with the UK's Royal Mail in getting the letter to him in the first place. Instead of addressing the letter to him c/o his publisher, I simply addressed it to him at the closest locality in England I knew of, and apparently it got to him, although as he noted in his reply, it had taken some time. So long that I had honestly forgotten I'd written in the first place.
Both of these facts - the casually terrible addressing and the fact that I forgot the letter almost the moment it was gone - bear witness to the fact that, while I certainly didn't mind and perhaps even hoped that he might read it, I had no reason to ever expect him to.
I wrote the letter because I had to, because something - just one sentence - resonated so deeply with me that it nearly made me get up and shout "Yes! Yes! THAT is how I felt!" I had to write about it, and who better to tell, even if he never saw it, than the very person who articulated my feelings? All the better since he's alive. Imagine if it had been Shakespeare, I would have had to write three letters. (Heaven, Hell, Luton.) (That's a little combined UK/Catholicism joke for ya there.) (Write for details.)
No, I'm not going to tell you much more about what I wrote, nor will I share with you all of how he responded. It is, as I said, personal. On both counts.
However, should you ever read something that you like, and it even occurs to you that you might wish to write to an author who has written something, be it a sentence, a paragraph, a trilogy... you might do well to let them know. They will appreciate it. And, judging by the last paragraph of Sir Pratchett's letter to me, they will very much appreciate that your appreciation is the only reason you're writing:
Thank you very much for taking the time to write to me, and especially writing to me not ending your letter with a request for a free book, a signed photograph, or a bookplate, but simply just to thank me. And that, sir, is why you are having one of the longest and most heartfelt replies to a letter that I have made for a very long time.
Will you hear back, as I did? I couldn't possibly say. But it's worth telling them anyway.