Around 7 years ago I looked into a grad program in CS with a bachelors in mathematics. I talked with graduate advisors from both my state university and Brown. Their requirements were similar: 4-5 undergraduate courses in comp. sci. and subject specific GRE. I believe the courses they listed were data structures and algorithms, computer architecture, programming language design, operating systems, and software engineering.

I think they've relaxed requirements a little but it's still not easy getting into comp. sci. from another field.

About work experience, the Brown advisor said that, for them, it's a mixed bag. A person from industry knows how to produce an application but there may be large gaps in knowledge. For example, a developer can go a long way using ArrayList in Java but not know a thing about it or alternatives, especially if code generators are involved.