Hi,
The "Unknow4 of GetVar called" message is a trace message printed by the VirtualBox's EFI guest-side code (in src/VBox/Devices/EFI/Firmware2/VBoxPkg/VBoxAppleSim/VBoxAppleSim.c). It indicates that OS X has requested an unknown property from some Apple specific EFI service. I get the same message in a Snow Leopard guest on Lion host setup, and the fact that VirtualBox's EFI does not offer an appropriate response to this query does not appears to pose any particular issue (well, in my setup anyway).
On the other side, there is a very long discussion over there that partly relates to this subject:
http://www.projectosx.com/forum/lofiver ... 008-0.html . This project aims at developing an alternative EFI to boot OS X; the very interesting point with that project is that they started it from VirtualBox's EFI code. I have not read the conversation throughly, but they seem to mention that VB's EFI might lack support of a newly added, Apple specific EFI protocol which would be required to properly launch OS X Lion. Note that I merely did a quick scan over the text, looking for keywords and interesting passages, so I may be a little off in my conclusion. I plan to also prepare a "Lion guest on Lion Host" setup in a few weeks, so I will certainly have to investigate a little more myself. Please post updates if you make any progress on your side.
If you are in a hurry or simply do not feel up to such investigation, you might consider simply using an alternative EFI; these EFIs are usually used in unauthorized setups (things like Mac guest on Windows or Linux hosts), but I don't think that using a third party EFI implementation to launch a virtual machine would in anyway be an offense to Apple's SLA, provided that the host is itself a Mac and that the guest operating system allows virtualization (that is true for Snow Leopard Server and all Lion).
Good luck.
-James
