Facebook could write their stuff in COBOL and it wouldn't matter to anyone else. Remember MySpace? It was written in ColdFusion, so I guess ColdFusion is a great idea!

Wikipedia's Mediawiki software is awful, and serves as a great example of how not to build an application. It makes WordPress look like a precision engineered Swiss watch.

Yahoo uses PHP because, like Facebook, they could make FORTRAN work in production if they wanted to.

pestaa's comment needs to be amended. It should read: "A sane engineer with a little bit of experience would not start off with PHP to build anything at all in 2013."

Facebook's former CTO has said that the only reason Facebook is still on PHP still today is legacy. It wouldn't be written in PHP if it were started today.

PHP once was the right tool for the job, but those years have passed. We have many better options now.

We have many technically cleaner solutions, but in the real world other factors, such as ability to quickly hire sufficient number of reasonably priced developers, often means a lot more than technical purity.

A sane engineer considers the full pictures before picking a solution rather than pick their pet languages just because it's nice and clean.

Were either of the first two started by "a sane engineer with a bit of experience"?

Inertia is powerful.

Perfect is the enemy of good enough. Doesn't matter what your site is coded in if it isn't revenue positive/have funding/etc.

I'm not sure where you got that from my post.

Though, to be honest, I don't think that using Play (today) or Rails/Django (yesterday) is sufficiently less productive to merit the technical debt you almost certainly will incur starting with a PHP stack. (And I am an ex-PHP person, to the point of hacking around in PHP core...that's a few months I'd love to have back.)