Colin sent this link and I thought it would be relevant to rant about it in a blog post
It's a very pretty (and technically clever) gimmick, so it might be appropriate as - say - part of a video game or movie promo website or similar system where it's more about presentation than content (and where there are at most 10 pages, not the hundreds in this monstrosity).
But that gimmick makes it much slower and harder to read and use content. I get about three short paragraphs before having to click a button and wait for a page transition. It's also less accessible. I can't use browser facilities to search within page - well, I can, but the page contains basically nothing on, whereas a typical display would only have 20 pages for this content, not 300 million or whatever. And also it doesn't support different screen sizes. (Maybe there is a mobile version but I mean, the normal version doesn't fit in narrow browser windows and doesn't take advantage of taller ones.) I can't bookmark pages using my normal bookmark feature [it wants to use offline storage, great, how does that work with my distributed bookmarks then], and I can't send links using the normal browser features - instead I have to use their special only-for-this-application share buttons.
As a toy? Really great.
As a way of providing information, teaching material, or any other useful content (including the content they're trying to put in it)? Absolutely terrible.
Basically this is probably fundamental usability mistake 3 on somebody's list of 20 things they learned about usability: use one technology to simulate another one, losing all the benefits of the technology you're actually using while not really having the advantages of the one you're simulating.
It's like building an MP3 player with an interface that looks like a Walkman, but where you actually have to rewind each mp3 after you finish playing it before you can play it again, and every time you play a different track there's a fancy animation of one cassette being ejected and the next one inserted. (Probably there is some company somewhere thinking 'wow! that would be a great idea'.)
Another real example is mobile games for touch-only devices which have an on-screen D pad...
By the way there is an appropriate place for 'page-turning' book interfaces: it's when you've scanned an actual book (or equivalent such as PDF file) so that there isn't a way to produce good quality, structured, scrolling HTML from that content.