Can you give an example? Things like the ISC dhcpd.conf are declarative, and the advantage that it "looks" like a programming language is that it's easy to read and see/form dependencies for complex setups--it's not just a big list of key/value pairs. That makes sense for a tool with a lot of capabilities. A quick glance at /etc doesn't reveal anything other than structured declarative files, key/value pairs, or delimited. There's a been a trend to use XML recently, which I find to be overly verbose for a configuration file, but even the XML-esque format that Apache uses is pretty much just a big list of key/value pairs.

sendmail.cf.

You got me there, isn't the sendmail cf syntax turing complete? Sendmail is one of the first things I remove if it gets installed by default. Got a more, for lack of a better word, "modern" example?

A lot of the more core/necessary configuration files on UNIX have pretty detailed man pages and documentation also. Which is definitely more than you can say for keys in the Windows registry.

What? You mean all of your config files aren't s-expressions?

I hope I'm not perpetuating a meme ;-)