One thing you can try is YAPE-Regex-Explain. It works like this:

use strict;
use YAPE::Regex::Explain;

my $regex1 = qr/^\s*$/;
my $regex2 = qr/^\w{1,}@/;

print YAPE::Regex::Explain->new($regex1)->explain;
print YAPE::Regex::Explain->new($regex2)->explain;
[download]

(Its a cool module from japhy)

UPDATE: Whoops, looks like everybody beat me to it!