How effective is facebook?

I have just finished reading the book by Ishmael Beah, a child solider in Sierra Leone, who shares of the horrors of war and the impact to young kids. Gut wrenching stuff which had me surfing the net at the finish of it wondering what I could do to help. I came across a couple of  “causes groups” on facebook.   Now maybe there are other factors going on like mistrust but what surprised me is the low level of donations given the number of members: 

 Invisible Children has 228,146 members and only $12,671 donated  

 Help the Invisible Children! 6,415 members and only $110 donated  

 Mothers Against Drunk Driving has 47,568 members and only $222donated

Facebook has brilliant mechanisms to automatically opt in friends which of course help drive up the numbers but really how active are those members. As any Direct Marketer knows quality not quantity has always been key to success. I think I read somewhere that members of facebook are not very committed. Do these donations suggest a rather passive involvement - or maybe it is just lacking credibility of cause. Either way be great to see web 2.0 help causes such as child soldiers achieve greater exposure and funding. By the way if you haven't read the book I'd highly recommend it - but be prepared to be "blue"