That sounds like the only remotely possible way to automatically classify modules. Other than that, all I can think of are social solutions such as asking people about their favourite modules in a place like this. The first mention I saw of WWW::Mechanize, f.ex, which hacker mentions, was the Perl Advent Calendar for 2002, which is basically Mark Fowler's "favourite modules this Xmas" site.

Makeshifts last the longest.