I'm no regex whiz, but I think you're making Perl do a lot of extra work with that regex to match table rows. All of those dot-stars means a lot of backtracking, I think.

Anyway, here's a slightly modified version:

    use LWP::Simple;
    my $user = shift or die "usage: $0 <username>";

    $_ = get "http://www.efd.lth.se/loginload.shtml"
        or die "Cannot get!\n";

    my $re = '<TR ALIGN=center>' . ('<TD>\s*([^<]+)</TD>' x 6) . '</TR
+>';

    my($load, $host);
    while (/$re/g) {
        $host = $1, $load = $5 if !defined $load || $5 < $load;
    }

    print "Host $host has load of $load\n";
    exec("ssh $user\@$host.efd.lth.se")
        or die "Can't exec ssh: $!";
[download]

Note also that I took out the exit after the exec--you don't need that, because exec never returns.

I think my regex might be a little more friendly, but I'm not absolutely sure. Note also that any regex solution will be less robust and less succeptible to HTML formatting changes than a solution like merlyn's.

Updated to test return value from exec, because I should've been more clear about exec and the possibility that it could return.