I agree 1000%! Many of my members don't realize that when they post their email address in the open, it allows spam bots to harvest their email address. One thing I do to help is similar to what you do. I use active text to replace the @ with a .gif image of the @ sign:
@|<img src="http://www.myforum.com/forum/images/general/default/atsign.gif">
That works if someone types in an email addy direct in a post but doesn't seem to work if they use the email icon in the editor.
