It's fine. I use it to run Solaris 10 and Windows XP on my MBP.

I ran VirtualBox on my MPB for nearly a year. It was a fantastic platform to run XP under for web development testing. It works very seamlessly.

Works pretty well on 10.5.7 with WinXP SP3 as guest.

I couldn't install a firewall for testing (Comodo CIS, it'll hang WinXP on reboot) on the guest w/o VT-X/AMD-V off. I hope they fixed it in this new version.