I recently did a 'Poll' on 'LinkedIn' about this topic that got 160 votes and generated some great conversation on this subject.
http://linkd.in/gHNOgt (Poll Results: Java won out)
I realized after the fact that I should have structured the question more specifically"
Ultimately, depending on what component of a trading system you are tasked with building (back office, front office, messaging system, quant. analysis, etc.) different technologies do things better than others, and there is no 'One Size Fits All'
Interestingly, if you look at the 'age' demographic of the respondents, C/C++ was typically those whom were a bit older 30+, while the younger generation tended toward Java, F# (OCaml), Or Python.
Also, it's important that many programmers whom have mathematical backgrounds tend to find 'functional' languages more useful as opposed to 'imperative languages'.
Both have their pro's and con's, but remember: functional languages tend to compile into faster byte-code, but maybe harder to adapt to newer technologies for the web.
For my part, I'm writing a limit-order-book in F#, Scala (Functional Java), and Python, and am going to study the results.