Having one's email address appear plaintext on a website is something most people try and avoid. Spammer's actively harvest email addresses from the public web and very few want their address on yet another spam list. In situations where it is unavoidable, people often use techniques like spelling out their address (Eg. user AT example DOT com) or adding in extra text (Eg. user_NOSPAM@example.com) or a variety of other approaches. Unfortunately these are easily detectable and extractable with some simple regular expressions and don't do much more than maybe prevent copy-and-paste of your address for legitimate users and maybe force spammers to add another regular expression to their script.
Some quick searches with Google shows how common these approaches are and also how easy it is to detect such patterns.
A slightly better approach, although not always feasible depending on the input restrictions, is to use JavaScript to write out the address. Something simple like:
<script>
document.write("us");
document.write("er@ex");
document.write("ample");
document.write(".com");
</script>
If a spammer were to process each scanned webpage with a JavaScript engine before extracting the addresses then the above wouldn't work, but the overhead (technically and CPU) is such that I don't see this happening anytime soon.
