you can't mix up private use with business use. If you use Debian, Kubuntu, CentOS etc you will always have a maintained OS for years. You don't have to pay for updates if you use them on your private computer.
In business you don't want to update your users desktop that often. People don't like changes ;-)
But you don't have to consider Linux on the Desktop, stay with MS, just change your server OS. People won't remark it and you will get much more possibilites in using different software =) Or just expand your MS environment with OpenSource software. There are millions of possibilities to make a admins life easier :-D