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>
It's possible that they set up some kind of revenue share w/ partner sites. Perhaps they get a share of the revenue from big players who feature a "Digg this" button. At the same time, the less traditional Digg users who come from sites like the WSJ or NYT are going to be more monetizable (for Digg) since they aren't going to be the standard issue Digg user/commenter who uses Adblock.
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>