According to some statistics gathered by the Gartner Research group, PHP is trending more towards being found in the enterprise:

A recent Gartner Research study found that 10 percent of the PHP community are corporate IT developers, and predicted that during the next five years, that number will grow to 40 percent. That's good news for PHP developers looking for corporate gigs--and very good news for PHP tools maker Zend Technologies, which cited the Gartner finding at the Zend/PHP Conference last week as evidence of widespread, more strategic adoption of PHP in enterprises.

Much of this has to do with Zend's products and their placement in more enterprise settings as well as the collaborations they've created with several key big-name players like Adobe, IBM and Dojo (as a part of the Zend Framework). There's also a mention of some of Microsoft's initiatives in the PHP community including work on the FastCGI component and a SQL Server driver for PHP.