"Lisp is worth learning for the profound enlightenment experience you will have when you finally get it; that experience will make you a better programmer for the rest of your days, even if you never actually use Lisp itself a lot."
If we're quoting that then we should also quote PG's objection to it: if Lisp makes you so much better a programmer, why wouldn't you want to keep using it?
Practical reasons: The language is great for enhancing your style but in practice it's been one of the hardest languages I've come across to make do real things. It interacts with the outside environment very poorly and more awkwardly. It's got multiple slightly incompatible implementations and it's library set is relatively light, green, wastefully overlapping and not very well maintained.
There's a reason Java won't go away and that's that it runs everywhere releatively easily and interfaces with stuff acceptably well.
Python is now doing a good job of this too.
Lisp has a looong way to go on this front and I do speak from some limited experience.
It's very pleasant if all you're doing is staying inside lisp and interacting only with your own code but as soon as it's asked to play nice with others it gets a lot less fun.
And staying inwardly focused, never looking out and never talking to anyone else ultimately means get very little real productive work done.
Please take a look at clojure. There are a lot of videos on youtube... there is a specific clojure channel. I don't recall the specific name, and work blocks youtube unfortunately.
Clojure runs on the JVM and has great Java interop, so you get the fun of lisp, and the convenience of all the Java libs.
ABCL, a common lisp running on the JVM is getting better and better by the release. It's java interop isn't quite as polished as clojures, but it is usable, and you get Common Lisp, which I like slightly better than clojure.
-- Eric S. Raymond