I have just subscribed to this website and as a test I searched for an ancestor in the 1871 census who I knew the whereabouts of. I have the family's axact details from the copy of the census in my local library. Imagine my surprise when I could not find him or any member of his family no matter what criteria I entered. Luckily digging through my records I found that I had recorded the reference, folio and page which I entered and found that the family who are quite clearly (to me at least) PUGH have been indexed as PUCH. No wonder I couldn't find them.
Now I know a work of this magnitude is going to have mistakes but one mistake in one search is for me 100% failure.
In future when I can't find someone how much confidence am I going to have in this website that they really aren't there.
For anyone interested the census ref is RG10/5655 Folio 82 Page 9 schedule no 44 (5 family members).