I had the same issue with BVU195 and Lion. The monitor was just black and would not work. I called Diamond support and they did not have any solutions. Finally, I upgraded to Mountain Lion, installed the 1.8 DisplayLink drivers and it worked.
http://www.displaylink.com/support/mac_downloads.php
Anybody else notice some extreme lag when using this product? I've had a ton of lag in both Windows 7 and OSX Snow Leopard and Lion, but I've scoured the internet and found zero posts of other users reporting lag issues.