Seemed to generally work OK for me with the latest CentOS 6 and VirtualBox releases. Not particularly fast to boot even with the VDI file on an SSD, 8 GB RAM and 2 i7 cores allocated. An equivalent setup for an Ubuntu VM is about 4 times faster to boot!
Apple menu -> About this Mac displays nothing and actually kicks in the session lock dialogue box :-( Configuring a UK keyboard seems tricky too (neither the European nor the ANSI options work), though I haven't looked at MultiBeast yet to see if anything fixes that.
Still, it's the first time I've seen a non-VMWare VM run Mac OS X, so that's an impressive feat in itself. Something the article failed to mention is that the space used straight after an install is 6.8GB - a useful figure to know if you're tight on disk space for your VDI file.