I remember a few years back, when I had a web-site I wanted to develop, that many people recommended I go the LAMP route. Unfortunately, I never got around to studying/practicing that.
I’m currently revisiting the web-site idea.
The web-site will be dynamic, transactional, and hopefully end up with around 1,000,000 pv/mo and 300,000 members within 18 months. Will LAMP adequately support a site like that (i.e. have you seen it under a site with those specs)?
Regarding PHP: I need to expand upon skills that will make me more marketable in the job market, i.e. would sticking with PHP make me more marketable, or are there studies suggesting another language/script would be more useful?
I would say, that this depends much more on your programming proficiency in the language of your choosing, than following the latest trend. If you feel comfortable with a certain environment you might want to stick to that. It reduces the probability of errors and makes development easier and faster.
That said, the answer to your question would be, that I consider the lower part of the LAMP stack (Linux, Apache, MySQL) still a very viable choice. As for the language: Possible alternatives might be Rails, Grails, Python, GWT, for larger applications Spring Web MVC, or even Perl, if you feel comfortable with it. The list is pretty much endless.