HTC EVO 4G Already Rooted
Not that Google probably minds too much. With the exception of slapping famed Android modder "Cyanogen" on the wrist (via a cease and desist letter) for bundling proprietary apps with his third party ROMs, Google has been very accommodating of the modding community.
In the case of the EVO 4G, it took three developers just a few hours to crack the smartphone and gain root access. They posted a craptastic video demo showing the hacked handset in full blur-o-vision, but outside of that, they haven't yet posted any details. Expect that to change once the upcoming smartphone reaches the general public.