The HDD in my Macbook recently died, so I put in an SSD. Consequently, I had to reinstall OS X, but an update was overdue anyway. Because I strongly prefer using Linux for serious work, I installed Xubuntu 14.04 on Virtualbox. The installation was a breeze. I like that Virtualbox now prompts you for an ISO image. The default settings are good enough, so the installation is highly streamlined.
There was just one issue I had to fix. By default, the Xubuntu desktop, as rendered by Virtualbox, is displayed in 640×480, and does not automatically adjust itself if you enlarge the window it runs in. The quickest way to fix this is to execute the following command in the console:
sudo apt-get install virtualbox-guest-dkms
This also installs all required dependencies. After restarting Virtualbox, the desktop of the guest OS will nicely be resized to any change of the window size in the host OS.
On a side note, it seems that the performance of the latest version of Virtualbox under OS X 10.9 is a bit faster than it was under OSX 10.6.