This first issue has been a problem during all 1.5x versions and it still remains. If Parallels 5.x is running and OS X display sleep engages, upon waking my MacBook Pro, I lose the ability to move my cursor to my USB-connected display (connected via VillageTronic ViBook). If I try to move my cursor to the USB-connected display, the cursor acts like it's bouncing into a wall. If I quit Parallels and OS X display sleep engages, I do not lose my ability to move to my cursor to the USB-connected display. The key here is whether or not Parallels 5.x is loaded.
This second issue appeared since the release of OS X 10.6.3, DisplayLink drivers 1.5 - 1.6x cause Parallels 5.x's screen to go black. I'm currently running Windows Vista Ultimate with my Parallels 5.x. After installing DL 1.5, Parallels loads, Windows loads (you can actually see the small Microsoft progress load bar for a few seconds), the window goes black, but you can hear the Windows startup sound, and then I'm left with a black non-functional window. If I uninstall DL 1.5, the problem with Parallels dissappears. Supposedly Apple made some siginificant graphics routine changes in 10.6.3. I'm now not able to use my USB-connected display at all because I have to be able to use Parallels (company uses Outlook).