I know its trolling to say "Eww, PHP", but every time these days I see yet another project that runs on it, a little part of me dies inside. :(
Why are you using PHP? Ruby/Python/Perl/A GUI in Visual Basic would be better!
Better for who? Look at the success of phpBB and Wordpress -- PHP is pretty much everywhere, and while maybe your favourite language is more elegant, PHP is largely ubiquitous.
But that aside, saying "its everywhere" is in my opinion the /poorest/ argument in favor of anything technical.
MySQL has their slogan as being the "Most popular Open Source database", which, by comparison to PostgreSQL's slogan "The most advanced Open Source database", awful.
If you're popular AND good, thats fine, but being popular alone is a poor metric.
PHP offers that, and I don't think I can name anything else that I can say that about.
On vaguely which subject, is there some documentation of the protocols anywhere? I had a quick look on the site and couldn't see anything like that.
Easy to deploy, but hard to find skilled hackers who will voluntarily work in it.
I tell everyone working on GNU social that we're going it for the betterment of the world, not their own personal situation. That means running it everywhere.
Look at the number of horrific security holes in phpBB and Wordpress. Every other release or so fixes some new flaw.
Note: I'm holding back a lot of language nerd rage, so I'm keeping this post very short.
Lots of webhosts are really sub-par, and tend to rip off their clients, and much of these same webhosts refuse to give root access, which is a pre-requisite for most of the non-PHP languages.
Sure, PHP will work on these platforms just fine, but as usual, the more people who produce PHP products, the more people out there who'll start dirty nasty webhosts trying to capitalize on that fact, perpetuating the bad hosting situation.
As for personal preferences from a technical standpoint, I'd have hoped somebody like GNU would have had the intuition to develop something well developed like a long-lived FCGI servlet application, which seems to be easy to do in every language except PHP.
PHP seems optimized for the developer use-case where "Something that runs perpetually and handles each request through the system chain" is "Too hard, and Too confusing", and instead they tailor to the 'Every request reloads everything from scratch' style of programming, which is in my personal opinion a design flaw.
Context: I was a PHP programmer for a while. These days I tend to become progressively more and more ashamed of that fact ( except in the obvious case here where I use it to bash it =) ). As a result, I don't frankly care what you use, I like Perl myself these days, but go ahead, use Python or Ruby, both increasingly more common. Heck, use C++ or Java for all I care, there are many decent systems, libraries and web frameworks in those languages ( that is, compared to the pathetic PEAR/PECL + Several dozen frameworks which each and every one of reinvent every wheel twice ), just use one, as long as its NOT PHP.
Go write the same thing in Ruby or Erlang or whatever if you can't stand the idea of software being written in PHP, or shut up.