David A. Wheeler: “This paper provides quantitative data that, in many cases, using open source software / free software is a reasonable or even superior approach to using their proprietary competition according to various measures. This paperâ??s goal is to show that you should consider using OSS/FS when acquiring software. This paper examines market share, reliability, performance, scalability, security, and total cost of ownership. It also has sections on non-quantitative issues, unnecessary fears, usage reports, other sites providing related information, and ends with some conclusions. An appendix gives more background information about OSS/FS.”
http://www.dwheeler.com/oss_fs_why.html