It had greatly improved our UI and sped up development.
They look ugly with Chrome + if fonts are not supported they don't show anything. At least if the image is missing you see X.
If you're designing things such that a missing icon causes the UI to be incomprehensible, you're probably designing it badly
The urge to plug your blog resist you must.
If there was a way to show off Font Awesome without providing a link to a case where I actually used it, I would. (screenshots won't be as effective since I incorporate on:hover effects.)
Icon fonts are so much easier to work with, I agree. That was a huge draw for us.
First, check that your server / the CDN is sending the correct MIME type for each font being served.
Secondly, the Access-Control-Origin-Header must be set to allow cross-domain resource sharing - Firefox doesn't permit cross-origin fonts by default, unlike Chrome and other browsers.