Here's a slide deck postmortem: http://www.slideshare.net/andreizm/the-good-the-bad-and-the-...

tl;dr: They made some bad decisions about Unicode and everyone got burned out.

They skipped 6 because 7 contains none of the Unicode changes and didn't want to confuse people.

It was a no-go. There was a lot of difficulties in getting it out the door, so I'm guessing they're pushing on with PHP7 to get rid of any social/political baggage that comes with the 6 release.

the non-unicode bits slated for 6.0 got rolled into 5.4, which was a pretty messy release given the extreme conservatism they adhere to even for major version changes.

If you do a Google search for "PHP6 Book" you'll see why they had to rename it:

https://www.google.com/#q=php6+book

Basically a lot of authors thought they'd get 'ahead of the game' and publish PHP6 books very early. If a 'real' PHP6 was released now, there would be confusion.

Politics. It should have been called PHP6. But to "avoid confusion" they skipped that number,which of course leads to more confusion.

This was exactly what I was going to ask.... reading these comments makes me dislike php even more...

It's out being almost as successful as Perl6 and Python3 :-)

e: Actually wasn't there a blog post posted to HN suggesting Perl skip to 7 too?