Side note: there's another attempt at something like MapReduce in Perl called DMap, written by Brad Fitzpatrick and built on Gearman. As far as I know, not available in packaged form - some links;

http://code.sixapart.com/svn/gearman/trunk/doc/overview.txt

http://brad.livejournal.com/2106943.html

http://brad.livejournal.com/2210265.html

That's distributed again though although I guess it would be easy to run the whole lot on a single system.