n00b alert! Sorry if this has been asked before.
I only recently heard about BitCoin, did some mining (solo and collective) and finally read the paper by Satoshi (more like glanced through it).
One of the requirements for "correctness" of the protocol seems to be that the majority of the network's computing resources should be under the control of honest owners.
In this light, the collective mining scheme seems very vulnerable. What if the maintainer of the pool goes berserk and starts tampering with the transactions? Or more likely, the controlling server is hacked and subverted? Isn't it risky for everybody if a lot of computing power is pooled together into one channel?