Your preferences tell you how to aggregate the preferences of everyone else.
Edit: This post was downvoted to -1 when I came to it, so I thought I'd clarify. It's since been voted back up to 0, but I just finished writing the clarification, so...
Your preferences are all that you care about (by definition). So you only care about the preferences of others to the extent that their preferences are a component of your own preferences. Now if you claim preference utilitarianism is true, you could be making one of two distinct claims:
In both cases, some "suitable aggregation" has to be chosen and which agents are relevant has to be chosen. The latter is actually a sub-problem of the former: set weights of zero for non-relevant agents in the aggregation. So how does the utilitarian aggregate? Well, that depends on what the utilitarian cares about, quite literally. What does the utilitarian's preferences say? Maximize average utility? Total utility? Ultimately what the utilitarian should be maximizing comes back to her own preferences (or the collective preferences of humanity if the utilitarian is making the claim that our preferences are all the same). Going back to the utilitarian's own utility function also (potentially) deals with things like utility monsters, how to deal with the preferences of the dead and the potentially-alive and so forth.
If my preferences are such that only what happens to me matters, I don't think you can call me a "preference Utilitarian".
In March 2009, Tyler Cowen (blog) interviewed Peter Singer about morality, giving, and how we can most improve the world. They are both thinkers I respect a lot, and I was excited to read their debate. Unfortunately the interview was available only as a video. I wanted a transcript, so I made one:
From there I pull back to saying "what does this mean about the problem of world poverty, given that there are, according to Unicef, ten million children dying of avoidable poverty-related causes every year?" We could save some of them, and probably it wouldn't cost us much more than the cost of an expensive pair of shoes if we find an effective aid agency that is doing something to combat the causes of world poverty, or perhaps to combat the deaths of children from simple conditions like diarrhea or measles, conditions that are not that hard to prevent or to cure. We could probably save a life for the cost of a pair of shoes. So why don't we? What's the problem here? Why do we think it's ok to live a comfortable, even luxurious, life while children are dying? In the book I explore various objections to that view, I don't find any of them really convincing. I look at some of the psychological barriers to giving, and I acknowledge that they are problems. And I consider also some of the objections to aid and questions raised by economists as to whether aid really works. In the end I come to a proposal by which I want to change the culture of giving.
The aim of the book in a sense is to get us to internalize the view that not to do anything for those living in poverty, when we are living in luxury and abundance, is ethically wrong, that it's not just not a nice thing to do but that a part of living an ethically decent life is at least to do something significant for the poor. The book ends with a chapter in which I propose a realistic standard, which I think most people in the affluent world could meet without great hardship. It involves giving 1% of your income if you're in the bottom 90% of US taxpayers, scaling up through 5% and 10% and even more as you get into the top 10%, the top 5%, the top 1% of US taxpayers. But at no point is the scale I'm proposing what I believe is an excessively burdensome one. I've set up a website, thelifeyoucansave.com that people can go to in order to publicly pledge that they will meet this scale, because I think if people will do it publicly, that in itself will encourage other people to do it and, hopefully, the idea will spread.
Immigration as an Anti-Poverty Program
I don't think we could have open borders; I don't think we could have unlimited immigration, but we're both sitting here in the United States and it hardly seems to me that we're at the breaking point. Immigrants would benefit much more: their wages would rise by a factor of twenty or more, and there would be perhaps some costs to us, but in a cost-benefit sense it seems far, far more effective than sending them money. Do you agree?
Changing Institutions: Greater Tax Break for True Charity
Millennium Villages Skepticism
Chinese Reforms
Military Intervention
Colonialism
Aid without stable government
Genetically modifying ourselves to be more moral
Problem areas in Utilitarianism
Is Utilitarianism independent?
Peter Singer: Jewish Moralist
What charities does Peter Singer give to?
Zero-Overhead Giving
Moral Intuitions
Improving the world through commerce
What makes Peter Singer happy?
Human and animal pleasures
Pescatarianism
(I also posted this on my blog.)