In July 2010 CentOS overtook Debian to become the most popular Linux distribution for web servers, with almost 30% of all Linux web servers using it. But in January 2012, it lost that position to Debian once again:
CentOS Popularity Trend
CentOS is one of the most popular Linux distributions in the hosting industry. Due to CentOS’ binary compatibility with RHEL, it is highly compatible with most Linux software. Most hosting control panels use CentOS as the preferred Linux distribution.