Rich Skrenta provides a useful counterpoint to the LAMP dogma by exposing some of the thinking behind Topix.Net's implementation. In a nutshell, Skrenta says dump the RDBMS and stick to flatfiles. Be as dumb as possible.
I think part of the reason that the LAMP model is so pervasive is that querying data falls out of shoehorning yourself into the relational model. It's hard to design, implement, and optimize a data query language. Also, Skrenta discusses how to deal successfully with concurrent data access, which is another thing DBs like Oracle and MySQL buy you, although at the performance cost of complete generality.
Interesting stuff though and worth contrasting against Phill G's teachings. Maybe the flatfile guys need someone to write, or recommend, a book on the topic.