A recent study of spam has found (see this link for details) that the majority of spam is sent to email addresses that have been posted on publicly accessible web sites (typically by searching through html code for "mailto" tags). Luckily the study also found that the email address harvesting programs that the spammers use are not particularly clever (like the spammers themselves) and by obscuring your email address you can a) stop new spam, and b) even reduce the amount of spam you receive.
This method does not impact the appearance or functionality of email addresses posted on web pages but does stop them being harvested by spammers.
Basically the technique involves substituting the ASCII value of the letter you wish to represent. Here's an example:
username@domain.com, (not a real email address!)
the obscured address looks like this:
username@domain.com
u represents the character u (this is because ASCII 117 represents the character u)
This technique should also be used for embedded mailto links as spam harvesters will find these as well.
This is an example of an obscured mailto link, note that it looks and behaves just like a normal mailto link from the users perspective but if you view the source it looks like this:
<a href="mailto:username@domain.com">This</a>
To make it easier for you to produce an obscured address, we've written a clever CGI to do it for you. Note that the script uses a random combination of ASCII and hexadecimal values just to further obscure your address.