All you need to know if that there is no way for all the machines on the bitcoin network to know when one event happens before another. This is important for financial transactions. The block cipher is a proof of work function which takes some effort to compute. Since this takes a predictable amount of time to compute it can be used to establish a sense of global time and order events. It doesn't always work right away, but eventually if someone tries to double spend a bitcoin one transaction will win out. This establish the trust necessary for bitcoin to work.
The problem is bitcoin can potentially be manipulated if you get a little bit less than 1/2 of the total network computational capacity.
I have been looking at the proof of work functions that are memory hard proof of work functions because they are more expensive financially to compute. There are tons of ASICs computing those hashes right now used in bitcoin which are far cheaper than any PC, but memory in an ASIC is always expensive. You get less of an advantage.
I think momentum proof of work function has potential, but I haven't seen any crypto-currencies use it yet. Let me know if you find one.
There definitely is a potential for safer currencies than bitcoin