Using md5 sum of file contents as key

[Justin Huff]

>>  Has any body used a function of the file contents as the key before?  Good
>>  idea/bad idea?
> 
> The FotoBilder software (powers PicPix.com and LiveJournal's ScrapBook
> service) uses this concept.  Although it doesn't use the hash as the

We're doing the same thing at Picnik.  It actually works great since we
often need to make cheap copies -- it basically gives us hard links.
Cleanup is handled as separate process that walks the files looking for
things that aren't referenced.

--Justin