In this new post to his site Mattias Geniar goes in circles...from Apache to Nginx and back in terms of how it relates to PHP.

As with many technologies, the PHP community too evolves. And over the last 6 or 7 years, a rather remarkable circle has been made by a lot of systems administrators and PHP developers in that regard.

He talks about the "early days" and the rise of Apache as the "A" in the LAMP stack. Then Nginx was created/released and PHP developers saw it as a viable option. He talks about how PHP worked with this server and the solutions that were found to "hack" them together. There were issues around the relationship, though, and - in the author's perspective - the circle has come back around to Apache, just with a bit more smarts about how it's configured.