>> Any tips on how to replace it?
> 
> What does it hurt if the hash value of a string does not remain constant 
> between runs of the application?
> 

In my case it's pretty bad. I use it in a command line utility to cache rake tasks. I create one cachefile for each directory, naming them using the String#hash of the full path (Dir.pwd.hash). If the hash is different the next time the program runs the cache lookup fails (and I get a new cache file instead of the old one).

So, I don't need anything fancy, just an equivalent to Dir.pwd.hash that stay consistent. Do I need to MD5 it? Feels like overkill. Why was this changed in the first place?