I am using Oracle VirtualBox now since a couple of weeks in order to establish if it can replace my VMWare Server.
I want to put down a couple of quick impressions - which will hopefully be followed up by some more insight.
It seems that Oracle VirtualBox is faster than the VMWare Server. Creating an image as well as starting it up and shutting it down are pretty fast. However if your machine is pushing the limits on memory the shutdown process of an image can easily take 5 minutes.
I have not yet found the possibility to create a disk file in chunks of 2GB. VMWare offered this OOTB. Now when I move my image from my Windows7 NTFS filesystem to the FAT external disk it complains about a 20GB file. More research is needed here.
I copied the images and gave them to some colleagues during several trainings. My experience is that the different laptops we use are not handled well by VirtualBox. E.g. I had to remove a network from the vbox-file in order to just start an image on a different laptop.
Stay tuned for more.