...subject says it all 
well, the code says:
<link rel="shortcut icon" type="image/x-icon" href="/favicon.png">
this means the favicon is inserted, and both the *.png and *.ico files are there ... can you take a screenshot and post it here?
also information about the browser and OS might help
What OS/Browser. I'm seeing it fine in FireFox on Win XP SP3 but not in IE8.
IE8 ... Microsoft playing tricks on the mighty HTML standard ... lemme check
/d
can you please confirm the favicon shows in IE now? there was a :
<link rel="shortcut icon" href="/favicon.ico" />
missing and IE seems to need it
I will do so, I was at work at the time on IE8 - I'll check when I get there...
ie7 is showing the favicon
Still not showing here at my work, on IE8 - I did some research, see this thread:
Several things in there to try - I would first try on the link where you have:
<link rel="shortcut icon" type="image/x-icon" href="http://arduino.cc/favicon.png">
...in the HTML - changing it to:
<link rel="shortcut icon" type="image/x-icon" href="http://www.arduino.cc/favicon.png">
Perhaps you could do that to the second link, or remove it entirely...?