That depends on what kind of business (or ways to make money) we're talking about here. For example, there are many web startups and web consulting companies t

That depends on what kind of business (or ways to make money) we're talking about here. For example, there are many web startups and web consulting companies that use typical LAMP stack or "light-weight" Java stack (Spring -IoC,AOP,MVC-, Hibernate/iBatis, Ant/Mavent, Hudson, MySQL/PostgreSQL). There are also other types of work that would require heavy help from the open source tools. One such example is embedded development. My friend works at Broadcom and he uses gcc, vim, ctags on day to day base. I'm sure companies that operate in hardware, system, and, network fields are also using open source tools heavily. The Russian developer, who used to work at Goldman Sach and got caught sending his work to some server, used a mix of Erlang, C++, and various other tools as well so I'm guessing those big guns at Wall Streets are using open source tools for their HF trading systems. Then there are your typical insurance companies, your typical hospitals, your typical small businesses, your typical banks, your typical grocery stores that would swear by Microsoft technology for their internal apps. I'm not trying to say that Microsoft is not suitable for "serious businesses". I'm looking at the trend around me and it seems that Microsoft technology appears in places where people need something quick to be done and would never add major features, instead just bug fixes and small polish here and there.