I've done a very quick test under OSX on my Mac Mini.

It generally behaves very similarly to under Windows 7, however it uses a bit more CPU and can't really cope with 720p at 1:1 (fine zoomed to 1:2).

The comparison is slightly skewed, as my Mac Mini is 2.0GHz compared to 2.2GHz on my Win7 laptop. But they normally feel about the same speed.

Apart from heavyweight video and slightly laggy window dragging you'd never notice it wasn't a native display. The adapter I've picked was the highest speced of the DisplayLink hardware, not sure if that makes any difference to the speed when running at 1920x1080 as I am.