I was nominated, but didn't do it.
I can think of other, more educational ways of raising awareness about cancer research. Also, before you do it, I'd read financial reports of ALS and other involved charities and see how much of the money is actually assigned to cancer research (hint: not so much).
Another aspect is egoboost. I don't really need to show everyone that I do things like that. I have one charity that I donate to every year, that I am sure is clear with their finances and the money actually go towards helping people (see
http://www.en.wosp.org.pl). I don't go to social media and record myself writing a cheque, making online transfer or post screenshots with my donation confirmation. I don't need to feed my ego, and from what I've seen in the videos that my friends post on social media, a lot of this stuff is just about egofeed: "Oh, look, I did the challenge too, I am so cool now! Now you do it, or else you'll just a !" kind of a thing.
I also believe in direct action rather than conscious soothing charity donations. Go outside and buy a nice meal for a homeless person, buy a 100 kg of dog snacks and deliver to your local dog shelter - you know, stuff that ACTUALLY does something.
I don't judge the people that fall for stuff like ice bucket challenge, to each their own. I do think however, that this particular initiative is pure waste of water, which is not very wise.
No disrespect to anyone by any means, but stuff like that is just against what I believe in life.
::EDIT::
Also, folks, please tread carefully with your opinions. Let's not be nasty to each other over this, as discussion about stuff like that can easily lead to accusations, insults and offensive actions. So please be respectful towards each other.