Shame on me, not visiting VirtualBox for long time make my mind make tiny error in making conclusion. This project is dead.
I’m totally wrong of course
VirtualBox 1.6 already released.
Click here to download
Some interesting feature in VirtualBox after acquisition by Sun :

Solaris and Mac OS X host support
Seamless windowing for Linux and Solaris guests
Guest [...]

Click here to read more from latest virtualbox