James Gosling blogs about the Sun-Microsoft agreement. It's an interesting read in that Gosling rebuts conspiracy theories that are apparently bouncing around the echo-chamber of the "M\$" mob (as a rule, I don't bother reading discussions where that "witticism" is common currency -- as much as I love the amateur programming community, I'm really only interested in people who are mature enough to understand that big companies are big companies, not soap opera characters). Apparently, the fear is that Microsoft has cleverly maneuvered into Sun into aggreeing to an impenetrable thicket of "compatibility" requirements, compliance with which will drain Sun's energy and innovation. (Ironic, huh?)
Gosling naturally says "We're not idiots. We don't blindly trust Microsoft. We're working in the best interests of our company and our clients." He doesn't address the question I've gotten left and right over the past couple weeks: "Does this mean we're going to see Java on .NET?" (Interestingly, no one's yet asked me "Does this mean we'll see C# or Visual Basic on JVM?").
I can't say with 100% certainty, but I've been discouraging people from believing in that. The class libraries are incompatible, and why go to the effort to port your class library to the other platform when your platform is the strategic foundation? (But might the agreement lower barriers to a third-party Open Source port of one class library to the other platform?) My guess is that 90% of the interoperability talk will boil down to WS- specifications: Web Service interop serves the interests of both companies.