If you use the snapshot manager under VirtualBox, this post may keep you from inadvertently losing your most recent work in your VM.
I had VirtualBox mostly working but I borked my VM hard (disk errors on the vdi file) by trying to run DPaint (yup old DOS program) under it just for kicks because running crappy old software that's not compatible with your current OS is an ideal way to test a Virtual Machine. Well, VirtualBox didn't like DPaint. Not only did it hang the VM instance, but the VirtualBox app itself hung and I had to kill the app. This ended up corrupting my VDI (virtual disk image) file.
No harm done though... I made a snapshot after my clean install, and then another snapshot after applying all the XP updates, ie 7, WMP11, antivirus, etc, etc. Just revert to the last snapshot and I'd be fine.
So I did a revert but thanks to their crappy snapshot manager, I actually jumped back past my last snapshot and ended up blowing away changes (which was several hours of updating, installing, and tweaking to get XP running just right after the clean install).
Turns out in VirtualBox, if you "Revert to Previous Snapshot", it deletes your current state *AND* your last snapshot and goes to the second-to-last snapshot (while destroying your last actual snapshot). If you want to just revert to your latest snapshot, there is something like "Discard Current State" which really isn't that intuitive. If you have something that could potentially throw away a bunch of work in a non-recoverable fashion, your choices and explanation of the choices should be a bit more clear.
In VirtualBox, snapshots are linear -- there is no branching. Reverting to a snapshot is a destructive process that cannot be undone, and it's confusing because you can either revert to your latest snapshot (which they call reverting to current rather than revert to snapshot) or revert to the snapshot before that (which throws away all current changes as well as throws away your latest snapshot). It's not intuitive and you can lose work.
VMWare is definitely nicer for snapshots. The have snapshot trees (they allow branching points for a VM) which you can selectively revert to any arbitrary snapshot in the tree. Moving to another snapshot is non-destructive and you can move back and forth between branches -- i.e. ABCD revert to C have ABCE and then go back to D.
Oh well... now that I know how the sucky snapshot editor in VirtualBox works, I'm less likely to screw it up in the future.
BTW, one other little annoyance on top of all this... if you do a disk-check at startup under XP with VirtualBox, for some reason, VirtualBox won't reboot itself after the diskcheck completes so you have to do that manually.