From Klaus Knopper:
unionfs is broken again, but not as heavily as in 3.9. If you install certain packages with dpkg or apt-get, a kernel oops can happen, though it doesn't freeze the system. This is quite bad for people (like me) who like to test-install new software on the live system, so because of this (and the prior reported bugs) there will be a hotfix of the 4.0.2 DVD soon (probably even before I get a chance to finish the CD).