Modders start your engines! HTC have released the kernel source code for both the HTC Tattoo - their entry level Android device - and the Sprint version of the HTC Hero. Each package is available from HTC's developer center.
As we've seen before, while it's been possible to mod devices without having public access to the kernel source code, once those files are out in the open it becomes a far easier matter. We're expecting to see some interesting tweaks, especially for the popular Sprint Hero.