Thing is, that under virtualbox, the boot time is supposed to be faster than in reality. I found it about 20% slower to boot than Win 7 under virtualbox. Plus it froze on the black screen twice and went to that white one once then froze again. Out of 6 boot attempts, it loaded correctly twice. I even tried reinstalling, but had similar issues.
I've had a lot of trouble with Windows in VirtualBox. XP is OK, although boots slower than it does on slower hardware when it's got 'direct' access. Windows Vista is just a trainwreck from start to finish in a VM from what little experience of it I've had in said VM, which while it's nothing to write home about when not virtualised, it at least behaves itself... most of the time.
I admit I've not tried Windows 7 in a VM, but Windows 8 is a law unto itself. The Consumer and Release Previews basically seemed to work if they felt like it - for example, I couldn't get Windows 8 to boot in a VM without some oddball tweaks (none of which I can remember right now, but I'm sure I found them floating 'round the 'net) but a colleague couldn't get it to work at all
I've not tried the RTM version, despite Technet giving me access to it back in August because I don't feel like using a license key up (Microsoft removed the 30 days activation grace period in Windows 8 ) for an OS that I'm probably not going to bother actually using. As I - and others - have said in the past... I'm sure Windows 8 will be great on tablet PCs (I'm debating getting a Windows 8 RT tablet to play with) but on my desktop I don't want fingermarks on my screens... even if they were touchscreens, which they aren't.
Perhaps I'm too demanding?