It's so funny how most people are fking clueless when it comes to math.
The 50% threshold is a STATISTICAL threshold and has no real meaning since an attacker could already with say 40% of the entire hashing power have enough of a statistical chance to realistically try to attack the integrity of the blockchain. When a pool has 50% or more it just means it easier to do then if it had 40% but nothing really changed.
Remember, it still takes 6 confirmations until a transaction is deemed valid, so even if someone has 50% of hashing power they still only have 1.5625% chance of getting 6 blocks in a row!
If a pool had 40% that number only goes down to: 0.4096% which is only about 4 times less likely to happen but already a very real threat.
As you can see, it's not a big deal, because the only thing that having so much power allows you to potentially do is confirm fraudulent transactions which becomes increasingly harder to do with increasingly more confirmations. It was already possible when deepbit had 30% or 40% or 45%, the only difference was the difficulty of pulling it off.
That's all in the regular process.
If deepbit decides to split off, they generate faster. And there the 50 % are magical, because it means it has more than the network it left.
That explains my advice: Don't worry, but watch carefully. We have to detect whether there is a block generating power mining in secret.
