And the regex engine is amazingly fast (there is one faster I believe). Try throwing a 20,000 item list at this little program, and then use the resulting regex to match another 20,000 items and see how long it runs (hint: not very, considering):

    #!/usr/bin/env perl
    use warnings;
    use strict;
    use Regexp::Assemble;
    my $ra = Regexp::Assemble->new;
    while (<>) {
        chomp;
        $ra->add($_);
    }
    print $ra->re . "\n";