You can encrypt mailto: links on a website, so that spiders can't detect them, with a simple javascript.
juergen [at] jumk [dot] de < click and test
<script type="text/javascript"> <!-- function UnCryptMailto( s ) { var n = 0; var r = ""; for( var i = 0; i < s.length; i++) { n = s.charCodeAt( i ); if( n >= 8364 ) { n = 128; } r += String.fromCharCode( n - 1 ); } return r; } function linkTo_UnCryptMailto( s ) { location.href=UnCryptMailto( s ); } // --> </script>