In my opinion, early on in your career the important thing isn't so much what language you are developing in, but who you are developing with. If you aren't in an environment where there are more experienced developers that you can learn from, find a different job. Over time you will probably move through several languages, but the core principles of programming apply to all of them, and learning how to think through problems from a developer's perspective is fundamentally important.

Another bit of advice would be to work in a position where you have your hand in all aspects of a project. That will help you decide if you want to focus on a particular subset of application development (i.e. back-end, front-end, UX), or if you want to move forward as more of a generalist. This decision will impact your future type of employment. Concentrating on one particular aspect of development will lead you towards larger companies and/or larger development teams. Being a generalist will lead you towards smaller companies or start-ups with smaller or no teams at all, as well as possibilities outside of normal technology companies (i.e. I am interviewing with a law-firm next week that needs a senior developer to create internal tools). I'm of course speaking only from my experience and making generalizations on that basis alone.

.NET MVC is a great first step on the corporate dev path. You'll mostly work in cost center departments (see article). It'll pay pretty well for a day job, but you'll have limited market leverage as a cost center. You'll have to go where the .NET jobs are, and that's mostly big companies that treat IT as a necessary evil.

PHP is a great first step on the indie dev path. You'll work in smaller shops, pay can fluctuate wildly, but at least you'll be a profit center. It takes a bit more hustle to manage your career but you'll be better positioned to hang out your own shingle later if you're interested in doing so.

A few years of enterprise work can be a fine starting point for transition into more indie dev, but you'll have to be honest with yourself about the trajectory you're on from one year to the next.

Entry level .NET (web) jobs may well be in IT departments, in a so called cost center, but I've have four web development jobs, all using .NET, and all of them have been for product companies, working on the core product, which was either sold on a SAAS model or DVD.

Yes, agreed. Well stated.

Anecdotally when I arrived in London I talked to a recruiter who claimed that PHP devs get payed less then .Net devs. One recruiter in one city so take with a pinch of salt.

My first job in the development industry was working as a PHP developer for a nine month internship.

Now that I'm graduating I received several job offers, most of them involved working with PHP again. However, I received two offers from two relatively large companies, one as an ASP.Net developer and the other as a Java EE developer. The salaries for these two jobs were quite a bit higher than the others and included great benefits too.

Again, I'm only a graduate so can't really give any solid answer as to whether you're sabotaging yourself by working with ASP.Net, though I doubt you are. Most decent employers will probably be more interested in ensuring you can program rather than focusing on what specific language you've been using recently. If they know you can program, they can probably assume you'll be able to apply that knowledge to a new language.