From Michael Anissimov on the Singularity Institute blog:
Thanks to generous contributions by our donors, we are only $11,840 away from fulfilling our $100,000 goal for the 2010 Singularity Research Challenge. For every dollar you contribute to SIAI, another dollar is contributed by our matching donors, who have pledged to match all contributions made before February 28th up to $100,000. That means that this Sunday is your final chance to donate for maximum impact.
Funds from the challenge campaign will be used to support all SIAI activities: our core staff, the Singularity Summit, the Visiting Fellows program, and more. Donors can earmark their funds for specific grant proposals, many of which are targeted towards academic paper-writing, or just contribute to our general fund
Landsburg's argument is sound, and I mostly follow it and occasionally try to sell others on it. But I can think of one exception, which is if the political power of an organization that you support depends on the number of members it has. So for example I pay membership dues to one organization that is not my main charity because I want them to be able to claim one more member.
And there is one place that I think Landsburg gets it plain wrong. He says*:
But if you think that the United Way comes tolerably close to sharing your values, but you think that they have better information than you do about relative needs and competencies across different organizations, then it makes perfect sense to donate to them, doesn't it?
*http://www.slate.com/id/77619/
I see ciphergoth already made my first point. Sorry about that.