1script - 11:02 pm on Apr 11, 2013 (gmt 0)
In the context of this discussion these would be a special case. Links from social media sites most often come through a non-indexable redirect URL, so, even though they are in the strict sense do-follow (as they appear on the originating page) nothing actually, well, follows because the non-indexable redirect kills it.
Social media's all I can think of
FB, Twitter and most other SM links I can think of are not worth the electrons used to transmit them.