Definitely an interesting read even for crypto dilettantes. Perhaps, especially for crypto dilettantes.
I took Rivest's Computer and Network Security class in college and the most important takeaway for me, far outstripping all of the interesting technical content, was "Don't implement crypto."
[edit: Thomas, thanks for the book recommendation below, I'll definitely grab a copy]
Everything that is wrong with "Applied" is right with "Practical". "Here are 4 modern block ciphers. We wrote one of them. Don't use it. You should use AES, but if you're a paranoid, use Serpent. But really use AES." It's great stuff, especially because if you really read it, you're going to end up not implementing crypto directly at all.