I used it a few years ago to write a reference implementation for a language feature whose real implementation was greatly complicated by the fact that it had to work in real time. I used Prolog to generate many thousands of test cases along with the correct result for each, then ran these through the real implementation to see how the results compared.

Prolog is not really a general-purpose language, so asking how it compares in "performance, development time, etc." is rather missing the point. If you have a problem for which Prolog is suitable, it will be easily the fastest way to solve the problem. But I wouldn't build a Web app in Prolog.

I'm afraid the only way to really get a feel for what it's good for is to write some programs in it. But it's a good tool to have in your toolkit.