In Search of Sun's Java Economics asks some interesting questions about how much revenue Sun derives from Java, or software in general, for that matter. Leaving aside the questions that raises about how investors should parse today's announcement, we can still talk about economic impact.
I do a weekly technology podcast with Scott Lemon and Matt Asay at IT Conversations. Today was our scheduled record date. Naturally, much of the conversation was about Sun's announcement (the podcast will be released next week).
Matt brought up something I hadn't thought of before: releasing Java as open source--especially under the GPL--might increase the sale of commercial licenses to Java that Sun sells. The logic goes like this: since the GPL requires "giving back," companies who might have winked at the commercial licensing requirements before will be less likely to now. Consequently they'll buy supported Java from Sun rather than risk having their IP contaminated (I'm using that word without prejudice) with the GPL requirements.
One other interesting note: Java wasn't open sourced. Rather the code was. What I mean is Sun still owns the copyright and trademark rights to the name Java and thus can control what can be called Java and what can't. For now, they're keeping the same tight restrictions on the Java trademark.