OTA will be available to all iPad2 and iPad3 owners provided they are running a 5.x firmware version.
If you use the OTA update method or use iTunes and select "update", it is only the OS which is updated. All your content, data, etc. remains intact.
If you use iTunes and select "restore", the device is wiped and a clean fresh copy of IOS6 is installed. Once complete, you have an option to continue as a new device or restore a previous iTunes or iCloud backup.
Note. If your iPad is currently jailbroken, the only option is to update to IOS 6.0 using the iTunes "restore" method, wiping the device and losing all jailbreak features in the process. See our Hacking Section for more info on that.
Hope that helps.