The problem is still here in the latest release.
I installed Avast on a clean XP x64 installation, Avast installed fine, I configured it, rebooted. But the boot got stuck on a black screen with only the mouse cursor, before the login screen.
I've experimented a bit and I think I narrowed down the issue to Virtualization. Infact, I went to Settings>Troubleshooting and disabled "Enable hardware-assisted virtualization". Rebooted and voilĂ , it worked!
So, until this gets fixed I advise that anyone with the problem tries to disable Virtualization.