Since early 2009, Displaylink has been selling pretty useful little USB-to-VGA adapters - USB graphics cards, basically. However, they had no Linux drivers and all questions about technical details were met with some boilerplate reply about "our patented compression technology bla bla".
So Chris Hodges and I decided to reverse-engineer the protocol. That turned out to work pretty well and ultimately resulted in a userspace driver library for Linux, libtubecable, which later was turned into a real kernel/Xorg driver combo by Roberto de Ioris, Bernie Thompson and others. Note that a couple of weeks after we published our first driver, Displaylink also published a userspace library called libdlo (which fails to impress me).
All of the technical information which we gathered is available in the wiki. I've given a talk at 26C3 about the entire process - see below for the video. Slides are also available. Moreover, we've published a technical paper with some additional details.
P.S. fun fact: although the Linux driver still doesn't support the Huffman compression mode, it's nevertheless faster than Windows.