I'm glad they're stopping development of Gobuntu, I think it's wasted time and effort. Let the Free Software nuts work on their strictly-free-software software.
Ubuntu is no worse than the other major distros for building clusters, and if you are building things for a fully virtual environment you might want to take a look at http://www.ubuntu.com/products/whatisubuntu/serveredition/je...
since it is designed for that purpose.
The nice thing about current (8.04) versions of Ubuntu server is the use of upstart which makes start up go fast. see http://upstart.ubuntu.com/