I guess most points have been made by this stage, but I would throw in an additional one. PHP and security have been mentioned and yes you can write insecure code in any language. Too many programmers get all religious about language, there is no best one it depends on what you're trying to do.
Having said all that I would highly recommend people take a look at the first few chapters of
http://djangobook.com/ and read through it. Yes it's a CMS system written in Python but I've found it so easy to generate web apps with it. I only mention this as many people have NOT suggested python for back end work. I've used django for numerous projects, large and small. One of my favourite ones, and perhaps relevant to eevblog people is one I run locally on my laptop and has a record of all my electronic component stocks. In Python and Django it's very basic but it's invaluable as I don't have to organise my components. If I'm looking for a P-FET I can look at a list of ones I have in my stocks. It tells me foot prints and most importantly where I put the dammed thing. I can even give it a kicad DOM and it'll tell me the price of the components.
That's just my itch and I scratched it, but python has the advantage of being both powerful and readable and thus far more maintainable then many other languages. And given Django's built in security I don't have to worry about the code I'm writing. Django takes care of all that stuff. IMHO ;-)