I've never been a master at the technical side of bitcoin. I know enough to explain to new people why they should embrace it in political discussions and that's about all.
Recently I learned that other data is stored in the block chain. I got to thinking: What stops someone from putting child porn for example and screwing over many people who would then have a copy stored in their blockchain?
I don't think this can be done on the Bitcoin blockchain, but there are other coins that have this feature built in. I have no idea about the ramifications of this though.