There are going to be some big changes at my company. And they will hardly be noticed. While the users will keep using their Windows XP/Office 2007 desktops, the backoffice will undergo a major overhaul. The Microsoft Small Business Server that, honestly, has served us well will be going away as we move to full featured systems without limitations.
I hired a consultant to design a system with high availability for mission critical functions and a 72 hour disaster recovery window. I stressed I wanted to use open source wherever practical. They have done the environment discovery and will be presenting their recommendations in a couple of weeks. We have talked about using a Windows Server as a DC to provide Active Directory authentication, Windows Software Update Services, DNS, DHCP, WINS, etc., We will also keep our Sharepoint Services 3.o intranet. Everything else will be running on CentOS5 servers. Email will be Kerio Mail Server, file sharing/storage will be Samba. Website will be Joomla. While the Kerio Mail Server is not open source itself, it does rely heavily on open source products such as Apache, MySQL, ClamAV, SpamAssassin, et al. I'll be extremely happy to see Exchange Server go and the end users will not see much difference at all with their Outook connected to KMS.
In the meantime, I'm learning CentOS. Most of my Linux work has been on Ubuntu both server and desktop. I set up a test server with Kerio Mail Server on CentOS 5.3 and I'm very impressed with the CentOS system. I'll probably replace the Ubuntu desktop on my notebook with CentOS to help me get used to the differences in file structure and package management.
The eventual goal will be to replace the Windows DC with Samba when Samba will handle Active Directory and WSUS. I don't know how we'll ever get off Sharepoint, though.