I am also experiencing frustrations with the Kensington SD400v device and Windows 8.
I have bought a few of these devices for our company.. On Windows 7 they worked relatively well, with only a few (acceptable) quirks.. Now with Windows 8 everything works except for the video (kind of a device killer). I have also tried the newest DisplayLink drivers (all versions) but to no avail.
I have contacted Kensington themselves to ask if the device will ever be supported on Windows 8, their response: The compatibility is under investigation at the moment, but unfortunately cannot be guaranteed that it will ever work. When it does work however, it will be published on our website.
That reads to me "buy our new products, this one will not be supported".
The thing is, this Kensington device is kind of good, especially when it comes to displaying the video.. This device is one of not many that can display full HD AND the notebook display without much performance loss (acceptable performance loss, no mouse delay).
Windows 8 is inevitable for us, due to the nature of our business.. So if you need alpha / beta testers: count me in! It would be a shame to have to have these docks collect dust
