I've used Perl... flexible but structures aren't rigorous or easy enough to build
I've used C#... fast to program and get things going, but I can't 'feel the deck plates' with the environment
I'm using C++...it is a bit slower to get things done, but I have more control over how things are built (templates, objects, functional programming, ...), and it is faster when running.  It is also 'funner' to use.

I like C/C++ for speed, but sometimes I prefer Java for rapid-ease of development.  The libraries are richer, and the IDEs are just plain better.    But in the end it depends on your application; I prefer multithreaded C++ for number crunching, and a GWT-based Java web UI for cloud computing!

I have coded in C++ professionally for almost 10 years and until recently would've considered myself a reasonably advanced C++ coder (via effective use of STL, template meta-programming, simple OO design heuristics etc).

However this article: http://blog.regehr.org/archives/213 has made me realise how ignorant I was in the possible number of potential cases where undefined behaviour could occur in my code (luckily none have yet been detrimental).

Whilst C++ offers a lot of power, a lot of responsibility is put on the developer to put in tests and handle cases to prevent undefined behaviour, which can amount to a lot of code for even the most trivial of things. Other modern languages such as Java and C# tend to solve this by throwing exceptions - better to crash predictably than give possible incorrect results or random crashing.

This is one of the many reasons I'm currently looking to move away from C++ as my main language of choice (to what, I'm still unsure).