The Zend Developer Zone has a review posted of a report that the O'Reilly Radar group put out concerning Open Source software and its place in the Enterprise business today.
It's not often that a report generates this much excitement but "Open Source in the Enterprise" says a lot of what needs to be said to C-Levels considering making the jump to Open Source.
Cal mentions one of the 6 factors that are driving more and more businesses to open source software (like PHP) - the community that surrounds them (how vibrant is it?). He also points out the concept of "vendor lock-in" and how open source can help companies accomplish it by ridding themselves of proprietary software. The report can be gotten from the O'Reilly Radar group for $399 for an individual copy or $995 for a sitewide license.