I really hate it when someone answers a question with "your question doesn't matter. What you should be asking is [whatever I think you should be asking] "

I assume the person asking the question has good reasons for asking it. If I can I answer. If not, I don't.

Coming to the question proper, there are often good reasons to ask if other people use / don't use a particular technology.

To answer, I use a custom variant of scheme to write machine- learning systems on a cluster of cots machines. It compiles down to optimized C, but I write in scheme.