If you are new to Android and if this is the first time you hear about CyanogenMod. CyanogenMod is a customized, aftermarket firmware distribution for several Android devices. Based on the Android Open Source Project.
Currently the CyanogenMod 7 RC2 (release candidate) is the second release based on Android 2.3.3 Gingerbread. It was released on March 8 2011. In a matter of 24-hours it’s been downloaded more than 150,000 times.
Using third party firmware like the CyanogenMod enhances the performance of your Android device and also it adds some features that cannot be found on the out of the box Android OS.
More about CyanogenMod
CyanogenMod Wiki
Cyanogen Forum
CyanogenMod Official website
If you have more question about this third-party firmware just drop by @ Pinoy Android Forum and I would love to answer your queries.