Yosemite Beta Driver works if...
 

Yosemite Beta Driver works if I restart without the extra display connected. Once Finder is loaded, then connect the display and it's all good.

At first (after upgrading to 10.10.1 and the beta DisplayLink driver) I just got the blank screen after restart but this process has got me going again.

Hope that helps somebody & thanks DisplayLink for the updated driver!

Diamond MM
BVUMD3

I found that this is not the case for me. new Mac Pro with dual D700, OS 10.10.1, 2.3b driver (Asus MB168+). nothing but black or serious glitched up completely unusable garbage on screen.