I disagree about the frictionless everywhere comment. This may be true for apps written with only the core of PHP but start to get into the extensions and you can get all kinds of incompatibility problems. God help you if you need to run Pear modules. I once spent two days with a rock star sysadmin getting the ecommerce engine Magento to install right on CentOS. I think we even had to edit a make file at one point.