Today BTCGuild (a mining pool) hit 48% of the network with some luck. I'd like ASICMINER to spread out their hashing power a bit to maintain a healthy net. With more units coming online and people's habit of choosing the largest pool (see DeepBit) I think it would be wise to take steps sooner rather than later.
Probably a newbie question - even if the pool went past 51%, wouldn't all the users of the pool have to switch to some sort of malicious code?