The official Ubuntu image ubuntu-lxde-14.03.06-p16g1.img has several issues e.g. no sound, no device node creation, poor desktop performance, instability on boot up...
So we have to apply these tips first.
http://elinux.org/Parallella_Speed_Up_UbuntuBecause Mandelbrot, Blobubska and aobench use native framebuffer, you have to connect HDMI monitor/TV and keyboard to the Parallella, and run them natively. (They won't run on a X Window or a VNC)