Sun Microsystems announced that the source code for Solaris 10 will be available as Open Source. From their website:
January 25, 2005 - Sun Microsystems, Inc. (Nasdaq: SUNW) today announced that the source code for Solaris 10 - the most advanced operating system in the industry - will be made available under the OSI (Open Source Initiative) approved Common Development and Distribution License (CDDL). The company has established a community Web site at opensolaris.org. Buildable source code for Solaris will be available at this site in the second quarter of 2005.
More info can be found in the press release and in opensolaris.org.
On the other hand Gentoo announced plans to add OpenSolaris support to Portage, being Portaris project a key component.