I have not used a lot of technology, but among the worst experiences was working with OR mapper. I don't think OR mappers are bad by themselves, but all the tutorials and entry level documentation drag the unknowing user slowly into a world of hurt. It looks super easy and super cool, but in fact if you don't know _exactly_ what's happening in the background you're about to deal with slow performance, terrible SQL statements, missing indices, etc. It makes shooting yourself in the foot a Starbucks-like experience, everywhere, all the time, and fast.

It's one of those promises that do not deliver the easy way despite most people advertising it like this. Except when you plan to write a book'n'author application with only 5 books and 3 authors. Yeah...