Supposedly Ubuntu will be shipping on 5% of new machines, which is about 
18 million:

http://linux.slashdot.org/story/12/05/07/2340247/ubuntu-will-soon-ship-on-5-of-new-pcs


There's this enthusiastic review for Ubuntu 12.04:

http://www.aboutlinux.info/2012/04/ubuntu-review.html


For October:  Quantal Quetzal...

http://linux.slashdot.org/story/12/04/24/2230248/code-name-theming-update-announced-for-ubuntu-1210

Mike