There is a recognized distinction here between a moral decision procedure and the criterion for an action to be right or wrong.
Pretty much all serious act utilitarians approve a rule-utilitarian decision procedure i.e. they recommend moral agents to follow the usual moral rules (or heuristics) even in those cases where the agent believes that departing from the rules would lead to better consequences. The justification for such a decision procedure is of course that humans are not ideal reasoners, we can not predict and evaluate all consequences of our actions (including others imitating us), we do not have an ideal, impartial conception of the good, and we tend to get things horribly wrong when we depart from the rules with the best of intentions.
Yet still, from an act utilitarian criterion for "right" and "wrong" a rule-violating action which maximizes expected utility is "right". This leads to some odd situations, whereby the act utilitarian would have to (privately) classify such a rule-violating action as right, but publically condemn it, call it the "wrong choice", quite possibly punish it, and generally discourage people from following it!
Yes, I was (improperly) ignoring the typically backward-looking nature of act utilitarianism. I kept saying "maximize expected utility" rather than "maximize utility" which resulted in true statements that did not reflect what act utilitarians really say.
I blame the principle of charity.
EDIT: And if I were being really careful, I'd make sure to phrase "maximize expected utility" in such a way that it's clear that you're maximizing the utility according to your expectations, not maximizing your expectations of utility (wireheading).
Despite being (IMO) a philosophy blog, many Less Wrongers tend to disparage mainstream philosophy and emphasize the divergence between our beliefs and theirs. But, how different are we really? My intention with this post is to quantify this difference.
The questions I will post as comments to this article are from the 2009 PhilPapers Survey. If you answer "other" on any of the questions, then please reply to that comment in order to elaborate your answer. Later, I'll post another article comparing the answers I obtain from Less Wrongers with those given by the professional philosophers. This should give us some indication about the differences in belief between Less Wrong and mainstream philosophy.
Glossary
analytic-synthetic distinction, A-theory and B-theory, atheism, compatibilism, consequentialism, contextualism, correspondence theory of truth, deontology, egalitarianism, empiricism, Humeanism, libertarianism, mental content externalism, moral realism, moral motivation internalism and externalism, naturalism, nominalism, Newcomb's problem, physicalism, Platonism, rationalism, relativism, scientific realism, trolley problem, theism, virtue ethics
Note
Thanks pragmatist, for attaching short (mostly accurate) descriptions of the philosophical positions under the poll comments.
Post Script
The polls stopped rendering correctly after the migration to LW 2.0, but the raw data can be found in this repo.