There are still customer rankings (the "Rate it" feature) and editorial reviews, but all the customer reviews are gone, the reviewer ranking is gone, and the helpful/unhelpful votes are gone.
A pity, as I was hoping to someday make the ranks of the top 1000 reviewers--my best rank was 2,171 in late February of this year.
This move seems to be really poor judgment on Amazon.com's part. I heavily relied upon customer reviews when making purchasing decisions, and I considered the reliability of individual's reviews by comparing them to other reviews by the same person. Now, that feature of Amazon.com is unavailable, as the huge existing database of commentary has been removed. Perhaps the "Customer Discussions" will replace it, but if the purpose is for people to go back-and-forth debating specifics of the content, rather than giving an overview and opinion of the work as a whole, it won't be the same.
It was also rather rude of Amazon.com to delete, without notice, the substantial contributions of its top reviewers. I was ranked only 2,171, but I reviewed 113 books to get there--and there were several million Amazon.com reviewers. Top reviewers reviewed thousands of books. That's an enormous amount of customer contribution to just throw away without notice or acknowledgment.
UPDATE (12:35 p.m. MST Sunday): As cowmix pointed out, the reviews are back. I spoke with a friend who works at Amazon.com, and he said that it is common for Amazon.com to make changes like this which are only visible to a test population of users, for a short period of time that's long enough to obtain information about how it affects customer behavior.