CyanogenMod is one of the biggest hacks to ever hit the Android mobile platform. It's got an estimated 500,000 users. Many Android programmers use it as a starting point for their own coding projects. And according to the project's founder, a number of Google employees have it installed on their Android devices.
Reasons to hack, or "root," your Android handset: Custom OS upgrades, PC tethering, full-phone SD backups. Reason not to: It's really scary. At least it was, until now.