Well, it has arrived! Functionality has gone live in OpenWorldCat which allows us to incorporate user views of materials. Check out the details and reviews tab here, for example.
We do not know how this will develop: we think it is really important to provide a central presence on the web where libraries and readers can engage in a conversation about books and other materials. We hope that this engages readers and libraries, and that we can collaboratively create something that it would be impossible for parties to create individually. Try it!
On a side-note, I especially like this initiative because it is another example of a collaboration between my research and production colleagues.
[Note: I originally used the Wiki word in the title of this post, because the underlying technology is Wiki-based - supporting Wiki-like functionality over structured data - and we use Wiki-like markup. However, we use it here to support a different type of application. In my excited rush to talk about it, I should have remembered this! Thanks to commenters.]
Update: here is a direct link to a review: