There is a small chance that something will break, which is usually either the wifi or graphics drivers on desktop systems.

Now let me ask you, is there any _reason_ for you to upgrade? Another poster mentions better laptop battery life but it could easily go the other way on some systems. Are you having trouble with any hardware? Unsupported webcam, etc? If not, then you're encouraged to upgrade the kernel as a learning experience but if your priority is stability and you don't have an evening to risk investing, then you should probably wait for Ubuntu to provide the update.