DisplayLink technology has existed for a while, and started appearing in more devices in 2008. It sounds like a very visualist-friendly concept – add extra monitors via USB – yet I haven’t seen it in action nor heard from any VJs using this hardware.
As to performance, DisplayLink is a software accelerated solution, compressing and sending the video data over USB. Various reviews have noted the performance hits this causes, and the DisplayLink Mac driver (released December 2008) page notes that the driver doesn’t support 3D acceleration. That aside, it could be useful for laptop performance or other compact projects where additional graphics cards won’t fit.