BYU’s Family History Archive is now online – how many family histories are available, I’m unsure of at this time – I believe that more and more will be added as time goes by.
It has a very simple, easy to use interface – most of us will be putting in a surname and then a geographic area (it also has advanced searches). Everything is in Acrobat/PDF format.
This is going to be a very important tool for many genealogists. It’s very neat – if you were to put in “Smith” as a surname and “Kentucky” as the Gegraphic Region, and then click on the first result returned, you’ll have an idea of what’s available. It apparently has the family histories archived and indexed in such a way, so that even if there is only a passing mention of a surname in a book, you’ll still be able to find it.
I commend the people behind this for going through the trouble of making it easily available.