hi madhatter,
its about 5 centimeters in diameter. it has a blue light at the base which u can program to pulse.
a rubber semitransparant base which almost sticks to your desktop.
the usb cord is kinda short around 50 centimeter but usb cords are very cheap these days...
u can turn the knob either way..
and u can even push it...
every move is programmable to a function key, a keystroke or something else.
ehm thats sort of my comercial for this little gadget
i never regretted buying it.
costs 39 dollars
more info here....
http://www.griffintechnology.com/products/powermate
only flaw i can emagine is that it sometimes doesnt recognize the powermate, but this is because i lug my shuttle around and plug it in after i turn it on
but when u pull out the usb cord and reconnect it works fine again...
ah and by the way...
u cant use it for videoscratching (which i had hoped for)
only for the sliders and all the other things that can have a shortcut key asignd.
greetz SuperficiaL...