I've just added it to my website (by removing the comment tag), and it doesn't really work as intended... Well, I don't think it does anyway. I've never used StumbleUpon, so maybe I'm using it wrongly??
Probably the reason why Rodolfo removed it from the code for now.
StumbleUpon sharer stop working long time ago and not only for Chevereto but for everyone else. In the past this worked to trigger an StumbleUpon add URL dialog:
Code:
ttp://www.stumbleupon.com/submit?url=%URL%"
But that doesn't work anymore and not even AddThis works properly with StumbleUpon. They ask for a customized JavaScript widget that I won't include by default but if you need it you can customize the theme and add it.