On a somewhat related note, I'm working on a method and system for collecting (as in downloading and saving) and storing a lot of the resources we've been identifying, which mostly means web pages, but also pdf docs.

What you'll find is that, over time, a lot of these things will disappear from the Internet via URL changes, site updates, and good old censorship. Most bad links are the result of site maintenance.

I've found a great tool for archiving web pages.