As you hint at the end, this strategy is more often used for evil instead of good.
For example, I did the same thing to buy a nice $650 briefcase the other day. It took a lot of effort to avoid thinking about SingInst, existential risk, and the future of mankind when using money for a personal luxury.
I worry you might be too generous. OTOH, any altruistic utilitarian should have their eyes pop out like corks at the idea of "too generous". On the gripping hand, this naive altruist is dead because they sold their vital organs for charity.
I say you've been awesome enough last time around and you can buy all the briefcases in the world as long as you keep it up. If your inner Bentham complains that you're spending nearly a dead kid on briefcases, tell it MixedNuts said you could.
On a completely unrelated note, what makes a briefcase worth that much?
My purpose in writing this is twofold.
First (chronologically: I thought of this earlier than the other), I want to discuss some of the pragmatic points in how I got myself to do it.
The most important thing is that I didn't try to force the decision through with willpower. Instead, I slipped it through with doublethink. I knew perfectly well - and have known for months - that giving money to SIAI was the right thing to do. But I didn't do it. I spent money on things like Minecraft instead.
But somehow I found myself at the donation page, and I didn't think about it. Or, rather, I didn't let myself think about the fact that I was thinking about it. I made a series of expected-value guesstimates aimed at working around my own cognitive limitations.
I chose monthly donation over one-time because $20 monthly sounds like about the same amount of money as $20; past experience with recurring donations suggests that I tend to leave automatic recurring donations in place for about a year or two, so that probably gained me about a factor of 20. Similarly, I chose $20 as the largest amount that wouldn't put me in serious risk of chickening out and not donating anything.
In order to pull this off, I had to avoid thinking certain true thoughts. Numbers like "$240 per year" only drifted through my consciousness just long enough to make the expected-value judgment, and were then discarded quickly so as to avoid setting off my rotten-meat hypervisor.
This was not the first time I decided that I should give money to SIAI. It was the first time I actually did give them money. (Except for that one time with the $1 charity-a-day thing, which actually might have helped with dissolving psychological barriers to the general idea.)
I think this is important.
The second fold of my purpose is to reinforce the behavior using the glowy feeling that comes from having other people know what an awesome person I am.1 Anyone else who's done anything worthwhile should feel free to post in this thread too.
1. It's true. Statistically speaking, I probably saved like a jillion people's lives per dollar. And more-than-doubled quality of life for a zillion more. Let me also note that you can get in on this action.
I know that sounds advertisementy, but... well, that's kind of the point. Practice Dark Arts on yourself for fun and profit.