Make sure to read about "umbraco Pro" as well - a commercial license bundled with superb support by the core team.
If you wish to use umbraco, but are uncertain that an open source license is optimal for your company, you can choose the umbraco Commercial License.
With a Commercial License you have complete freedom over the software including rebranding the software without any of the restrictions that may apply in an open source license.
A Commercial License is a perfect match if you have an existing commercial application that lacks CMS functionality. With easy skinning of the umbraco ui and fast integration with your existing authentication models, you can offer your clients a complete integrated web solution with a minimum of effort.
Commercial Licenses are available in single site and server versions, for more information, don't hesitate to contact Niels Hartvig for more information.