Tim O'Reilly of oreilly.com fame, has observed that the true killer app of open source is not an application at all. Rather, it is the LAMP (Linux, Apache, MySql, PHP/Perl/Python) platform and the web services build on top of it. Google, Amazon and Yahoo! are the best examples of successful Open Source projects, rather than OpenOffice or the KDE desktop.
I agree with him. And it is not only the obvious Internet companies that use LAMP, any bigger corporation in need of a flexible solution that uses lots of servers in a custom configuration obviously can gain a lot by using an Open Source solution. Knowing how things work internally, being able to mix and match components within an OS and the power to completely rewrite pieces of the OS is going to come in handy if you're trying to set up a computer system to power a international trading platform. Or if you want to mass-produce a computer-like consumer device, it really makes a difference if you don't have to pay a fifty-dollar license fee to MS. On the other hand, if you're a small company, doing some in house development, you'll probably stick with some MS Office/VBScript combination. Linux is hard, Windows is easy. It is sad, but still true, whether your configuring PC's or developing an invoice system.
My point is, only the big corporations have enough resources to profit from free software. In a way, this is only logical. Open Source software means free as in free beer, but more so as in free speech. The license fee is usually only a small part of the cost of deploying software. The freedom that Open Source software offers goes way beyond that, but it doesn't mean a lot if you can't program, just as the freedom of press isn't worth that much if you can't read or write. And only the big companies write their own software. Maybe that is why Big Blue likes Linux so much.