Several of the original enumeration books of the 1851 census for several areas around the city of Manchester, England were badly damaged by flooding at the Home Office in London. Many pages were not considered worth microfilming, many of those that were filmed were illegible and the books were not made available to the public because of their very fragile nature. The records of over 200,000 people were effectively lost.
In 1991 a team of volunteers from the Manchester and Lancashire Family History Society completed a painstaking 14 year project to examine these records at the National Archives in London to extract these names and achieved a surprising 82% overall success rate.
More details of the project and a name index have just been made freely available by the Manchester & Lancashire Family History Society at: http://www.1851-unfilmed.org.uk/.
The site is still being worked on to improve its usefulness.
My thanks to Frank Mitchell for telling me about this great new resource.