Thus the disclaimers.
then you should probably consider that "free" time
However, do note that the generalization of that argument would allow a vast number of posts asking for the use of "free time" on various less effective causes. Other matching grants (this one is expiring now, but there will normally be something in the same ballpark), petitions, tasks on Mechanical Turk, and so forth could be summoned.
If there were 100 such posts each month responding to them would clearly on average be a drain on your other activities, requiring willpower/glucose to deal with, etc. Likewise 50. As we get to smaller and smaller numbers the costs are harder to see, but they still exist (this is the flip side of computing benefits to marrow donation by subdividing the aggregate effect;). Likewise, there are costs in terms of page space, taxing some users (non-Americans who can't donate, people who don't want to see such things), and the like.
You estimated a generous 25% -- I don't know, but I'll go with that. In that case, the time would probably be worthwhile.
"Generous" means "probably lower." A bit of Googling suggests that the gain of some transplants (which are nonetheless performed, and thus good candidates for "marginal transplants") is only a few life-years (i.e. sub-10%) and regression (based on general medical ineffectiveness, and overestimation of effects in the medical literature) would drive a best guess lower.
If you can spare 3 minutes to swab your cheek that you would not otherwise spend to earn 3 minutes' worth of money and send it to the Against Malaria Foundation, then you should probably consider that "free" time.
I understand the thought, but it also illustrates the point about accuracy: the actual costs in time from mailing, reading instructions, etc, are more than 3 minutes.
With 20 minutes of work (it took me over 12 minutes to fill out the form, 10 minutes reading the commitment and FAQ, plus the time in mailing, swabbing, more forms, etc) plus rather than 3 required to register, a 1 in 540 chance of donating (less if European ancestry, more otherwise), and a benefit of 10% of a malaria victim saved (after costs of further testing, possible surgery, drug effects, etc) we get the equivalent of a 1 in 1800 chance of saving a life per hour of work. Using AMF to convert between money and time (and AMF itself is not at the frontier; if it is that effective then GiveWell itself has been doing more on the dollar by leveraged direction of funds to AMF, not to mention other causes), that's a wage of $1.11 per hour, less than one can earn on Mechanical Turk. Taking into account more "drag factors" would probably further worsen the picture.
This all makes sense to me. Was I mistaken in posting this? I might say that if things like this happened once a month, the morale bonus from fuzzies would be worth the cost to me, but I don't think that would scale up. But if no-one did things like this, the registry would be empty of donors, and a world where everyone pumped their free time into money for malaria and neglected all other worthy causes seems distasteful to me.
This topic is not really related to the things normally discussed here, but I think it's really important, and it might interest Less Wrongers, especially since many of us are interested in ethics and utility calculations that are essentially cost-benefit analyses. Bone marrow donation in the United States is managed by the National Marrow Donor Program. Because typing donors for matching purposes can be costly, they often require people signing up to donate to pay a registration fee, which probably prevents a lot of people from signing up. These costs are being covered until the end of the month by a corporate sponsor, which means that right now, all you need to do if you live in the US is go to http://marrow.org/Join/Join_Now/Join_Now.aspx and fill out a simple questionnaire. You will be sent a kit to collect a cheek swab, and then you will be entered into the donor database. Doing this does not require you to donate if a match comes up.
The reason I think this might interest Less Wrongers is that this is a really cheap way to improve the world. According to their website, about 1 in 500 potential donors are actually asked to donate, so registering doesn't actually make it all that likely that you will be asked to do anything more. If you ARE a match for someone who needs a donation, the cost to you is at most the temporary pain of marrow extraction (many donors are asked only for blood cells), whereas the other person’s chance to live is much improved. This looks like a huge net positive.
Unfortunately I only found out about this a few days ago, and it only occurred to me today that this might be a forum of people who would respond to the argument "you can make the world better at little cost to yourself." However, I ask that you go to the website and spend a few minutes signing up. This is like buying a 1 in 500 lottery ticket that SAVES SOMEONE’S LIFE. If the Singularity hits and an FAI can generate perfectly matched marrow for anyone who needs it from totipotency-induced cells, that will be wonderful, but this is a chance to make sure one more person gets there.