The CPU auto speeds to save power. You'll see it at 528Mhz sometimes and 300 odd othertimes. There's some apps in market to control the CPU in other ways if you prefer.
Rooting won't increase the cpu speed or change its scheduling
DROID still isnt hacked, but thats because its running the latest live android OS so we cant use bugs already discovered in older kernels.
The hero (and most HTC devices) can be rooted by bypassing security using a gold card (an sdcard wit a specially generated key on it).
The behold was rooted with the same exploit that was used on other 1.5 systems from quite some time ago. The persistant root uses that same exploit, but just some trickery to make it run on every boot.