Large scale environments where real performance matters.<p>I wrote a system the has to handle 4 Billion transactions a day and a peak of 45,000 per second. And has to respond in 10ms or else the results of the transaction are discarded.<p>I wrote it in PHP so it would be easier for my team to maintain but it would not scale beyond 4,500qps then I re-wrote it in C as an apache module and it now scales to 25,000qps per server.<p>Sometimes you just have to write stuff in C. I've been writing in C for 28 years. I write other languages as often as I can but once in a while I have to go back to C to get something done. Right tool for the right job!
Startups doing hardware projects which use embedded controllers: I <i>think</i> most 'firmware' as its called is written in C. Also, a bit unrelated but 'Verilog' and 'VHDL' are C-like low level hardware description languages used especially for prototyping via FPGAs.
I work at Kiip, where we write primarily in Python, Erlang and C. We have built several in-house analytics systems than can handle upwards of 300K qps. We are hiring too: <a href="http://kiip.me/jobs" rel="nofollow">http://kiip.me/jobs</a>