The great thing about reading this comment thread is that I basically already read it a couple of weeks ago, because a friend of mine (David Gerard, of Wikipedia, RationalWiki and Rocknerd Internet fame) let me preview his forthcoming e-book _Attack of the 50-Foot Blockchain_. There's a whole section in there about smart contracts, Ethereum, and The DAO that goes over much of what commenters here have mentioned ("non-reversibility, till it's our money at stake", the requirement that everyone write and read code perfectly, the problems with the very idea of immutability in contracts, etc.)
If people are interested, it's on Amazon: http://amzn.to/2trOjJS (I have no financial interest in it, but I bet a lot of people in this thread would enjoy reading it and/or writing long diatribes on why he is wrong about everything in it.)