"Linux feels like it was written. Solaris feels like it was designed."
Neil A. Wilson wrote an interesting article why he choosen Solaris as is favourite operating environment: “Why i like Solaris”. It´s an article about some features of Solaris, but there is one paragraphy that summarizes an important reason of my choice for Solaris many years ago as well:
Linux feels like it was written. Solaris feels like it was designed.. While I think that Sun’s development processes can sometimes be a little heavyweight, and I think that Sun is trying to retain too much control over OpenSolaris, there is a lot to be said for having processes in place to guide development.
This is the basic difference. Linux is based on the concept “Okay, you can develop a feature and we will see if we integrate it into the mainline code.” Opensolaris works differently in this area. The concept of PSARC may look as an heavyweight process for an opensource operating system, but it´s the reason for “Solaris feels like it was designed.” as the documented review of the design and the analysis of the impact to the whole architecture is the beginning of all code in Solaris.