Haskell can be fantastically fast (rivaling C for some tasks), and nothing can beat it for writing parsers. Relying on lazy IO can be risky if you don't know what you're doing, but I've been able to write log parsers that can crunch multi-gigabyte files as fast as my SSD can read them, all without ever going over 4MB of RAM.
Plus it's incredibly stable. Once you learn to avoid a few sharp edges (head, !!, etc.) you should never encounter an exception at runtime. Literally never.
I guess there are domains where it's adequate, but what are those?