I find it's still a fairly good indicator. Last time I was looking for a new author I went back and compared the author's average rating. Authors I like were 4+. Authors I think are OK scored about 3.5. Authors who I won't read again were generally 3 or so.
Perhaps 'useless' is a strong word. It's good for getting a general idea but too many books hover around the 4 mark. Whereas with IMDb anything 6 and above is worth the risk.
