The Rocks Linux Cluster Distribution picks CentOS to build it's new distro on: http://www.rocksclusters.org/Rocks/
RocksClusters joins these other projects as picking CentOS for their base OS:
SME Server: http://contribs.org/modules/phpwiki/index.php/Upcoming%20Releases%20page
OpenFiler: http://www.openfiler.org/sponsors/
Asterisk@Home: http://asteriskathome.sourceforge.net/
We at the CentOS project are happy to see other Open Source groups use our distro as a base for their products ... they just verify our belief that CentOS is the best "Free" Enterprise Linux solution available.
Thanks,