When it comes to open source software, the question that needs to be asked today is not which businesses are using open source but rather which businesses are not.
Yep have to agree with this - as a small business owner I know it makes a difference not having to shell out huge amounts of money for license fees and upgrades for software. My business runs comfortably on Linux, my accounting package is Turbo cash, just recently switched to LibreOffice from Openoffice and my e-mail runs on Thunderbird! Add to that a host of other freeware tools and programs and I can pretty much say Open source has given me a competitive business productivity suite and platform while saving me tons of cash!
Who says no to opensource? (Except for Microsoft and Apple and so on) It has been proven over and over again, you save a lot of money, and get better features some times.
Dont 100% agree with the above statements - I consult at a number of large enterprise businesses here in PTA/JHB and most of these companies still have huge windows/solaris/etc environments with no real plans to "open source" them.
There will always be companies who will stick to their infrastructure, be it Windows or whatever. It's probably easier for a new start-up to use open source than it is for an existing company to change its infrastructure to accommodate and adapt to the open source systems.