joel on software has quite an extensive article on unicode. the article does a nice review of UTF-8, encoding issues and debunks some nonsense about unicode. its also got a bunch of good resource links peppered throughout the article. all in all, a very good read.
he points out one interesting issue about PHP, which i never knew because i don't use it, it doesn't natively support unicode. its got a couple of functions to encode/decode UTF-8 but all i can say about that is "bah, humbug".