According to Gartner, almost all businesses will use open source software:

Open-source promoters have welcomed the endorsement by what is seen as a conservative commentator, but predict the changes will go further than Gartner assumes.

“By 2012, more than 90 percent of enterprises will use open source in direct or embedded forms,” predicts a Gartner report, The State of Open Source 2008, which sees a “stealth” impact for the technology in embedded form: “Users who reject open source for technical, legal or business reasons might find themselves unintentionally using open source despite their opposition.”

=> Gartner: Open source will quietly take over