If you are learning PHP in 2013, yes, you are wasting your time. PHP's killer feature was (not any more) $5 web hosting, where you could upload your index.php with FTP and you're done with deployment. This is no longer the case. PHP stands for (at least used to) "Php is a Html Preprocessor", but at some point it turned into a general purpose programming language, largely as an afterthought.
Yes, you can learn web programming using PHP and that skill won't be wasted. But a lot of the PHP specific issues you'll be dealing with is just going to be a waste of time. There is a lot of WTF issues in PHP that you'll inevitably stumble into. This will be a major factor in the time wasted.
In addition, the world is full of bad PHP code. Yes, there is good PHP code too but the proportion of bad code is probably larger than in other languages. This will mislead you and make you learn bad practices more than you would perhaps do if you'd be learning another language. These are cultural, not technical issues.
For a beginner, I would recommend Python or JavaScript. Neither of them is my favorite language, but Python is rather beginner friendly and JavaScript has a special role since it's the language that web browsers use. Ruby is popular too, but in my opinion it has more traps a beginner could stumble into (not so much for an experienced programmer).
For learning purposes (not production code), I would perhaps even recommend staying out of big monolithic frameworks like Django and Rails and learn how things work internally. You'll get a better idea from HTTP and other web technologies if you build your own "framework" from building blocks like WSGI, SQL alchemy and a templating engine like Mako or Mustache (these are Python-specific, for another language, you'd pick other tools).
This is my recommendation for a beginner looking into web programming and my motivation is to keep a beginner away from bad technologies that may teach bad practices.