I’ve seen a lot of these that are bloated/less effective/inaccessible, so I might as well put this out there. It’s simple enough to modify if you’re comfortable with Javascript.

Markup: <a href="mailto:john{@}example{.}org">john{@}example{.}org</a>

(function(){
  var a, i = 0, o = this.onload;
  onload = function(){
    o && o(); // run the old window.onload if existed
    while (a = document.getElementsByTagName("a").item(i++))
      if (0 == a.href.indexOf("mailto:")) {
        a.href = a.href.replace(/[{}]/g, "");
        a.innerHTML = a.innerHTML.replace(/{(.)}/g, "$1");
      }
  };
})();

Minified 234B:

for jQuery 150B: