I have noticed quite a few video artifacts on screen when using three displays on my MacBook Pro.
I have a new MacBook Pro with three NEC 22" monitors. Two monitors are setup with DVI to HDMI cables and the third is DVI to DVI. With all three monitors plugged into the Plugable and running the supplied black thunderbolt cable, there are a large amount of white blocks that appear on screen.
I’ve downloaded the latest DisplayLink drivers. Each monitor runs native resolution of 1680x1050.