When I was developing my arduino based website I learned about favicon.ico.
So I thought to reuse the arduino.cc/favicon.ico on my arduino.
This tuned out to be a bad idea because it took the arduino a very long time to send the icon (I have to slow down sending due to hardware setup)
Therefore I looked at some size of the favicon.ico of some popular sites and came up with the following table
arduino 367.958 bytes
mozilla 2.550 bytes
microsoft 3.638 bytes
Not being limited by my lack of knowledge of this feature it looks to me like there is room for a performance increase of the arduino web site