Well, the open Java Community Process had already opened up Java considerably, but now Sun have made the right decision in releasing many J2SE and J2ME components under the GPL licence. This article by Allison Randal of O'Reilly summarises it well: O'Reilly Radar > Java released as Open Source
The obvious follow-on question is when will Solaris be released under GPL, and in fact this was asked at the launch event and the answer was a definite maybe:
Posted by mofoghlu at November 14, 2006 09:04 PMThe main launch event was led by Jonathan Schwartz and Rich Green, with pre-recorded video segments from Richard Stallman, Eben Moglen, Tim O'Reilly, and others. At the very end, Schwartz asked Green if OpenSolaris would also be released under the GPL. He gave the best answer possible: that the community feedback from choosing the GPL for Java has been positive, so they are indeed considering the possibility of future GPL releases. It's worthy of note that the license chosen is specifically version 2 of the GPL without the often-added text "any later version", which means that Sun has reserved the right not to upgrade to version 3 of the license. Simon Phipps commented that Sun is happy with the GPLv3 process. Chances are that Sun will upgrade when the time comes, but it's a choice that strengthens their seat in the discussion over the future shape of the GPL.