My best guess at productive subgoal for FAI is development of decision theory along the lines given in the last post, in order to better understand decision-making and the impossible problem in particular (how to define preference given an arbitrary agent's program; what is a notion of preference that is general enough for human preference to be an instance).
About a year ago I was still at the "rusty technical background" stage, and my attempts to think about decision theory were not quite adequate. Studying mathematics helped significantly by allowing to think more clearly and about more complicated constructions. More recently, study of mathematical logic allowed me to see the beautiful formalizations of decision theory I'm currently working on.
I can't tell you that studying this truckload of textbooks will get any results, but reading textbooks is something I know how to do, unlike how to make progress on FAI, so unless I find something better, it's what I'll continue doing.
Ambient decision theory, as it currently stands, requires some grasp of logic to think about, but the level of Enderton's book might be adequate. I'm going deeper in the hope of developing more mathematical muscle to allow jumping over wider inferential gaps, even if I don't know in what way. Relying on creative surprises.
This post enumerates texts that I consider (potentially) useful training for making progress on Friendly AI/decision theory/metaethics.
Rationality and Friendly AI
Eliezer Yudkowsky's sequences and this blog can provide solid introduction to the problem statement of Friendly AI, giving concepts useful for understanding motivation for the problem, and disarming endless failure modes that people often fall into when trying to consider the problem.
For a shorter introduction, see
Decision theory
The following book introduces an approach to decision theory that seems to be closer to what's needed for FAI than the traditional treatments in philosophy or game theory:
Another (more technical) treatment of decision theory from the same cluster of ideas:
Following posts on Less Wrong present ideas relevant to this development of decision theory:
Mathematics
The most relevant tool for thinking about FAI seems to be mathematics, where it teaches to work with precise ideas (in particular, mathematical logic). Starting from a rusty technical background, the following reading list is one way to start:
[Edit Nov 2011: I no longer endorse scope/emphasis, gaps between entries, and some specific entries on this list.]