almost never. but there are some that are at least as good. like with trainspotting, i couldn't tell you which i love more; what they did with the film adaptation of that was really well done. and it's a very different film from the book in many ways, which works to its advantage.
it all depends. Some are worse, a lot worse. Some are a lot better then reading the book. It all depends on if the director is trying to closely follow the book, or if he thinks he can do better himself and rewrite it to suit him.
Like anything, it depend on the piece created. Often, the book is better than the movie, but there are examples of the opposite. The Godfather is a great example; it started as a fine book, but will justly be remembered as an excellent movie.
the movies will always lack details, weather important or minimal to the story line, in them so in that sense the books will always be better. but there are a few instances where the book wanst that great to begin with and the move then outshines it, or they are both equally great.