In all honesty, I've been reading about this for a short while and I don't understand. But I'm not sure that matters at all.
It seems there is a general agreement that there is a flaw in the Bitcoin model which means that in a circumstance of an organisation gaining 51% of the computational power (as just happened) the entire currency is compromised.
This is doubtless just another glitch as we progress to a crypto-currency but in the short-term, it really doesn't help.
This is the sort of issue, I think, that could keep regular folks from adopting the crytocurrency. Imagine sitting your parents down and telling to shunt their bitcoin into litecoin until GHash is less powerful and thus bitcoin is safe to use again. Not going to work.