Some interesting comments on the differences between Red Hat and Ubuntu:
Red Hat is committed to Enterprise Servers
Ubuntu is committed to the Desktop
Another big draw for the corporate crowd is the Wubi Windows installer, new to this release of Ubuntu, which allows users to download and test the Ubuntu desktop on their Windows PCs without repartitioning the hard drive. Shuttleworth said getting corporate end users comfortable with a new desktop is critical for its evolution.

See the Red Hat article here (http://blogs.zdnet.com/open-source/?p=2310)

and the Ubuntu article here (http://blogs.zdnet.com/open-source/?p=2335)