It's heartbreaking to go back over these pages and discover that some links are already broken (eg G&S at Google Books).
Maintaining FW links is comparatively trivial: almost everything's keyed to FW1 pagenumbers. In comparison, Ulysses links have to be handcrafted and so individually stained with the maintainer's blood.
The ways of Google are mysterious and terrifying-- presumably they post generous previews of in-print books until the publisher complains, or makes some new deal. So all we can do is cross our fingers that what's linkable today will still be linkable tomorrow.
I'm concerned that some of my mp3 links have suspicious ID numbers in their urls that hint they're volatile, and I may have to go back and redo them.
Archive.org is also a cross-your-fingers deal, I fear.
Youtube like GoogleBooks is vulnerable to copyright trolling.