Prompted by a question posed by one of my colleagues today, "has anyone ever used Lisp?", I surprisingly found myself being the only person that had.
I played around with it many years ago after being inspired by Eric S. Raymond's seminal article, "How to Become A Hacker" in which he explained that "getting" Lisp is equalivent to finding programming nirvana.
Whilst I didn't quite reach those levels, I found that using Lisp was a great learning experience. Despite it being half a century old, it is still a relevant language today; the online Practical Common Lisp book contains examples of a spam filter, an ID3 tag parser and other real-world examples.
The following two links are for the curious who might wish to try it out: