Unless you know or plan to learn about lisp, it can be hard for you to maintain or modify the code. I am building an HN clone in Python (I'll probably make a PHP/SQL version too) and will open-source it in a couple of months. Stay tuned.
There were a couple of clones, but none took off really. The most prolific one seems to be newmogul.com by nickb, focused on business and economics. Nickb has all but disappeared since, and Newmogul is no more, but some of the patrons moved on to http://markenomics.com.
HN is written in PG's own dialect of lisp, http://arclanguage.org and source code for vanilla version of the site is included with arc distribution. There's no reason not to hack together a clone and get a taste of the language.