Hej and welcome to Ask Ubuntu!
The overall market share of Ubuntu Server is about 9.3 percent and counting, popular sites using Ubuntu include Wikipedia, The Internet Archive, Buzzfeed and others.[1]
Ubuntu is and always will be free[2], the same goes for the server version.[3]
There are paid-for enterprise support options available[4], but the base product (Ubuntu itself and the bundled software) won't cost you a penny, even if you'd make millions of dollars using it.
There is free community support here on Ask Ubuntu and on the Ubuntu Forums, as well as the Official Ubuntu Documentation and the Community Help Wiki to help you with all Ubuntu related questions or problems, completely free of charge.
Further advantages of Ubuntu (and, to be fair, GNU/Linux in general) include Freedom (no restrictions, no vendor lock-in...), Security[5] and cost-efficiency (no license fees, free upgrades, lower maintenance cost).
Also, the included package management system (APT, Advanced Packaging Tool) and the many freely available administration tools make upgrading and deploying software as well as other maintenance tasks across many computers and company networks easy and painless.
Further reading
References
- “Usage statistics and market share of Ubuntu for websites”, W3Techs, January 2014
- “About Ubuntu”, Ubuntu.com
- “Ubuntu Server - for scale-out computing”, Ubuntu.com
- “Server Management”, Ubuntu.com
- “Security/Features”, Ubuntu Wiki, May 2014