Checking for spam in perl scripts

One thing I noticed is that a lot of spam bots post junk strings to the form, and you can catch some of them.  By testing for "multi-voweled" strings - strings with 5 vowels in a row, or more, you can guess that the submission is junk. 

Here's a short snippet of code which shows how to do this check (this assumes "$field" is an incoming field value you want to check:

if($field =~ /[bcdfghjklmnpqrstvwxyzBCDFGHJKLMNPQRSTVWXYZ]/) {
    print "<script>
      alert(\"Nobody has a Name like that!\");
  history.back();</script>";
    exit;
  }