While investigating a friend’s report of ext3/InnoDB corruption in a Ubuntu VirtualBox guest, when his OS X host machine crashed, I discovered that by default, VirtualBox does not do anything about IDE Flush Cache commands. A risk of this is that your journaled and transactional guest systems risk corruption if the host crashes. (For longer reasoning see that forum post.) It’s as if you were running them on broken hardware.
Even if you’re only doing development in VB – to reduce the chance of a nasty surprise, I recommend you disable the IgnoreFlush option in VirtualBox. See “Responding to guest IDE flush requests,” in the VirtualBox manual.
This issue may also affect other virtualisation hosts.