Canon has issued the latest build of its EOS 550D (Rebel T2i) firmware, 1.0.9. It specifically repairs a peculiar issue with occasional, but rare, tone jumping within some images.
According to the documentation, 1.0.9 fixes "a phenomenon in which tone jumps become noticeable in some images, depending on the shooting scene, when shooting with the Auto Lighting Optimiser settings (Low / Standard / Strong)".
It's a doddle to apply the new firmware: Just download the required file from the Canon website, extract it to a cleanly formatted SD card (either through a memory card reader, or attach the camera to your computer with a USB cable), and access the update via the camera's menu system. It takes around 30 seconds to complete.
Do make sure that you have a full charge in your battery - you won't want to suffer a power failure during the installation.
Also, ensure you read the complete instructions on the Canon site first.
Have you found any other issues with the 550D? If so, let us know in the comments below...