I've heard scattered bits of accusations of misdeeds by BP which may have contributed to the spill. Here's a list from the congressional investigation of 5 decisions that BP made "for economic reasons that increased the danger of a catastrophic well failure" according to a letter from the congressmen. It sounds like BP took a bunch of risky shortcuts to save time and money, although I'd want to hear from people who actually understand the technical issues before being too confident.

There are other suspicions and allegations floating around, like this one.