I read an interesting post on The Unofficial Footnote Blog not long ago, comparing the ongoing census projects of FamilySearch with Footnote. Not surprisingly perhaps, a number of commenters questioned the purpose of additional census projects, particularly of Footnote, when Ancestry.com seems to have such a lock on the completeness of the data.
I wondered this myself, but interestingly enough, was able to find some ancestors using the Footnote census for 1860 who are eluding me in both the 1850 and 1860 censuses on Ancestry. Once I had the citation in Footnote, I could browse to the page in Ancestry and find the elusive ancestors. (I like using Ancestry to track records and compile complete-ish timelines for the folks I'm working on.) Seeing the corresponding transcription in Ancestry, it was pretty apparent why I hadn't found them -- the surname had been transcribed as "Greenley" instead of "Greenleaf" and the frustrating thing was, the original image was pretty readable both in penmanship and imaging.