RC 2 of CM 9 should be pretty stable, and perfectly good to be used as a daily driver. It will allow you to get rid of Samsung's TouchWiz Nature UX, and replace it with a stock UI with some added functionality. If you have strong desire to mod your Galaxy S III by installing a custom ROM, but are somewhat new to all of this, it's good to know that CyanogenMod is the most popular and fully-featured custom Android ROM.
It is believed that this Release Candidate will be the last RC, and the next version of CM 9 will be the final one. The final release is expected to come out in about two to three weeks. Meanwhile, members of the team are already working on CM 10, which will be based on the latest Android version - 4.1 Jelly Bean.
You can find more info about CyanogenMod 9 and the ROM itself by following this link.
source: CyanogenMod via AndroidAuthority