This is a very interesting debate. I wrote a longer answer with some experiences I had while mentoring a colleague into Mathematica, but apparently google groups lost it.
The core point I'd like to make is that the greatest things about Mathematica are, in my opinion, its language and its principles. I think Mathematica structure is far truer to mathematics than other languages. The missing bit for me is deployability; Mathematica would be more useful to me in my work if its deployment aspect worked more like a true programming language, like java applets or iPad apps, without restrictions to import user data and so on, which is a similar point others have already made in this thread.