As for Lingua::Stem, I just tried out a few examples from Stemming Performance that you linked to:

use strict;
use Lingua::Stem;

my $stemmer = Lingua::Stem->new();
my @words   = qw/maintained maintenance environment experience/;

my $stems = $stemmer->stem(@words);

print "$_ " for (@$stems);
[download]

The output was:

maintain mainten environ experi
[download]

So it appears to have failed to merge maintain with maintenance(?), but correctly dealed with the environment/experience difference described on that page. This is the first time I've looked into the subject, so I could be a fair bit off the mark :).

As for other (sort of) related modules, I've found TheDamian's Lingua::EN::Inflect to be useful (and fun) to use on occasion. I'm not sure how much that applies to your question though.

++ for an interesting thread, I look forward to hearing what your conclusions are.

Edited 18 June 2002 (footpad): Fixed broken </code> tag.