It's an awesome series of books. It was real popular when it first came out, was on the NYTimes best seller list forever but for some reason i rarely ever meet people who've really read through 'em.....
It's strange, I ought to love these books. I really like stationary (especially the cute and often odd japanese style) and I love to write letters and I've thumbed these books numerous times in the bookstore but something always made me put them back.
Though I am intruiged by his latest book "Urgent 2nd Class", which I'll probably pick up when I see it for sale secondhand. Hmm... I'll have to revisit his other books again.
If you like those books you might want to look for an odd little collection called "Postal Seance: A scientific investigation into the possibility of a postlife postal existence".