Is Illumos 'good' for OpenSolaris?
The ability to fork an application is one of the great strengths of open source software. If a project isn't going in a direction that users/developer want - then a fork provides an option.
Illumos - a new project that is aiming to build open source components of Oracle's openSolaris is not a fork -- at least that's the direction that the project leadership told me last week. What Illumos will provide is a way for users/developers to eventually create a fork of openSolaris.
Yes, it's good news for openSolaris users that there might one day be an option - a fork - that could meet needs that the main project does not. However, it is important to remember that openSolaris (and Solaris) are valuable operating systems because of the tremendous amount of capital/research that Sun (and now Oracle) are investing in the platform.