The color screen shots are great and I've been able to use this book to get some ideas and inspiration for sites I've built. That being said, here's my beef:
1) Why organize by color scheme? There have been lots of complaints that these books come with little explanation as to why the chosen sites were selected. An easy way to remedy this would be to organize chapters in such a way that focuses on key aspects: navigation, layout, use of graphics/photos, color schemes, interactivity, etc.
2) The disk that came with it doesn't work much of the time, and none of the Flash sites worked.
3) For sites that have dynamic elements, like rollovers, etc., it would have been nice had they shown an example of the behavior in the screen shot.
4) The websites featured weren't that great. Hey, everyone has his/her own taste, but when I got it (which was before Index 6 came out), it didn't represent some of the more interesting things happening in web design (in my opinion).
5) The pages are thick and due to its shape, the book won't stay open to a page and is kind of a pain to handle. This may seem silly, but it was an irritant for me with a desk full of papers.
In using this book, I often found myself endlessly flipping through pages, flagging certain ones with coded post-its, reading "nav" or "photos." Because of this impracticality, I mostly ended up going back to the growing number of websites devoted to collecting and presenting (with screenshots!) contemporary, well-styled websites. These frequently include discussions of certain trends, like color choice, web logos, layout configurations, etc.
This book is nice to have around, in spite of its problems. Its limitations may be a good thing, in that it forces you to narrow your likes and dislikes within a limited collection of ideas. The Internet, in its infinitude, can be paralyzing. This helps you step back for a second and just consider the visual elements of a home page.
I have not looked at Index 6, but its likely to repeat some of what I think are errors. One that's inherent: very soon these books become outdated. I'm not sure they're useful enough to keep buying them.