ServerSide has an article on IBM's support for PHP. As a Java developer, I don't think that this is anything to worry about, mainly because I specialize more in back end server side Java that JSPs, struts, etc. (although I also do a lot with the presentation layer).
Actually, I like PHP a lot for smaller web apps that don't have to scale, etc. I installed SugarCRM (a CRM system written in PHP) for a customer last year, and liked it.
With light weight communication there is no reason why the presentation for web application can not be done lightly (e.g., CherryPy for Python developers, Rails for Ruby developers, PHP, etc.) with back-end processes written in heavier weight languages like Java or Common Lisp.