We've made some fixes recently that solved black screen issues we saw here. Assuming you have Linux hosts here are test builds with the fixes included:
Linux 32: http://www.virtualbox.org/download/testcase/VirtualBox-4.1.9-76144-Linux_x86.run Linux 64: http://www.virtualbox.org/download/testcase/VirtualBox-4.1.9-76144-inux_amd64.run
Note that you'd need to update guest additions also. Let me know whether it solves the black screen issues for you.
