Does this really make a difference? Are there any studies of gmail with addresses that are hidden vesus those with plain text email addresses for bots? The critical number is the false negative/positive amount, not the absolute number of spam. And surely spammers can already find ivan[at]tipjoy[dot]com
A good way to stop spam is using JavaScript to ROT13 encrypt the address. This way you can display it in plain text, but when a bot looks to search through the source on a page it just sees JavaScript jibberish.
TextMate can do this for you automatically.
For a site, you could just have a small back end script that looks for an email address in standard format and then encrypts it. You get something like this:
<script type="text/javascript">document.write(
"nneba\100nangbzlnqf\056pbz".replace(/[a-zA-Z]/g, function(c){return String.fromCharCode((c<="Z"?90:122)>=(c=c.charCodeAt(0)+13)?c:c-26);}));
</script>
