From Deadline Hollywood:

The long respected film critic really stepped in it this week when he wrote a long negative review of a movie without revealing until the very end that he only saw the beginning of a 99-minute film before walking out. (Ebert wrote at the finish of his critique: "The rating only applies to the first eight minutes. After that, you're on your own.") Here is Ebert's own blog defense: "My editor argued that in my Tru Loved review, I should reveal in the first paragraph that I drew the line at eight minutes. I protested. That would pervert the flow of the review. Everything after would be anti-climax. What I was trying to do was recreate my thoughts as I watched the movie, and show them leading inexorably to my eventual decision. But was I placing my regard for my prose over the rights of the movie? I hope not. I hope the review truthfully records the process I went through." Sorry, but his argument is lame to the extreme. How can you base a review on 8 minutes of a 99-minute film? Most of us could name hundreds of terrific films that started out horribly. Conversely, if people had only seen the first few minutes of Godfather Part III, it would have looked like a worthy final installment to Coppolla's mob masterpiece. I think no reviewer should dare critique a film without seeing the entire film.

Here's the review
http://rogerebert.suntimes.com/apps/pbcs.dll/article?AID=/20081015/REVIEWS/810150277/1023