Samsung Galaxy phones are the current leading lights of the Android world, and as you would expect for the bestselling devices, they have been embraced by the Android development community. However while it is as trivial as always to flash a ROM to a Galaxy device it does come with a bit of a kicker.
Samsung has a flash counter on each of its devices that registers whenever a custom firmware has been flashed. In the event of a warranty claim for a hardware fault on a Galaxy you would want to restore the original firmware and unroot the device, but this flash counter would show that the phone had, at some point, been modified. This in turn can potentially cause issues with warranty claims.
The solution to the problem is to use the Chainfire app Triangle Away (£1.99 from the Play Store), which resets the counter to 0. You can use the app alongside Odin to reflash a stock ROM, and that should give you a device that appears to be clear and unmodified.
However, the app itself is not without the significant risk of bricking your device, and it is important that you read and follow the full instructions in this thread: http://bit.ly/OZ1Bzs before proceeding. If you have a phone running 2.3 or earlier then purchasing a USB Jig from ebay may be a safer option.