I relied on Google Books' digitizations of 17th century rare books constantly while in grad school for history; probably more than half of the texts I cite in my academic publications were accessed via Google Books. But lately I've noticed that many of the rare books I relied on are no longer available to read (they're clearly still living somewhere on Google's servers since you can search for snippets, though).
Anyone know why this happened? It shouldn't have anything to do with lawsuits related to publishers since the books I'm talking about are centuries old and housed in places like the British Library, which one would think would be committed to making them publicly available. In some cases (like my weird little specialty, 17th century Portuguese apothecary and drug manuals) I'd say the decrease is on the order of 80-90% fewer texts available.
Luckily HathiTrust largely makes up the difference, but otherwise this shift would be kind of a catastrophe for me as a researcher. There are dozens of times when I my choices were either "access this rare book via Google Books, or fly to Europe and look at the closest physical copy, which happens to be in some obscure library in Belgium/Lisbon/Rome/Budapest/etc."