I'm a huge fan of icon fonts, but I have a nit to pick with the HTML they chose.
<span class="icon-sm icon-org"/>
That is not valid HTML. The <span> element is not a self-closing tag, so the slash is essentially ignored [1]. Fog Creek's blog is XHTML, so the tag makes sense there, but Trello is HTML5.
[1]: http://dev.w3.org/html5/spec-author-view/syntax.html#syntax-...