I know I'm 5 years late on this but on the offchance someone sees this, I just want to mention I found Yvain's/Scott Alexander's essay on the subject incredibly useful*.
The tl;dr: Use universalizability for your actions moreso than direct utilitarianism. His suggestion is 10% for various reasons, mainly being a round number that's easy to coordinate around and have people give that exact number. Once you've done that, the problems that would be solved by everyone donating 10% of their income to efficient charities are the responsibility of other people who are donating less than that amount (I'd also suggest trying to spread the message as much as possible, as I'm doing here).
Of course it'd be better to donate more of your income. I would say that if feeling bad about donating 10% causes you to donate more, then... donate more. If it just causes you to feel like you'll never be good enough so you don't even try, it's useless and you'd do more good by considering yourself completely absolved. 10% is also incredibly useful for convincing people who aren't already convinced of unlimited utilitarian duty to donate to efficient charity.
*http://slatestarcodex.com/2014/12/19/nobody-is-perfect-everything-is-commensurable/
During a recent discussion with komponisto about why my fellow LWers are so interested in the Amanda Knox case, his answers made me realize that I had been asking the wrong question. After all, feeling interest or even outrage after seeing a possible case of injustice seems quite natural, so perhaps a better question to ask is why am I so uninterested in the case.
Reflecting upon that, it appears that I've been doing something like Eliezer's "Shut Up and Multiply", except in reverse. Both of us noticed the obvious craziness of scope insensitivity and tried to make our emotions work more rationally. But whereas he decided to multiply his concern for individuals human beings by the population size to an enormous concern for humanity as a whole, I did the opposite. I noticed that my concern for humanity is limited, and therefore decided that it's crazy to care much about random individuals that I happen to come across. (Although I probably haven't consciously thought about it in this way until now.)
The weird thing is that both of these emotional self-modification strategies seem to have worked, at least to a great extent. Eliezer has devoted his life to improving the lot of humanity, and I've managed to pass up news and discussions about Amanda Knox without a second thought. It can't be the case that both of these ways to change how our emotions work are the right thing to do, but the apparent symmetry between them seems hard to break.
What ethical principles can we use to decide between "Shut Up and Multiply" and "Shut Up and Divide"? Why should we derive our values from our native emotional responses to seeing individual suffering, and not from the equally human paucity of response at seeing large portions of humanity suffer in aggregate? Or should we just keep our scope insensitivity, like our boredom?
And an interesting meta-question arises here as well: how much of what we think our values are, is actually the result of not thinking things through, and not realizing the implications and symmetries that exist? And if many of our values are just the result of cognitive errors or limitations, have we lived with them long enough that they've become an essential part of us?