Do you like book trailers?

Reading a book is a very personal experience. While we read we imagine the setting, the faces, even the voices. Whether the author gives us a lot of visual information or not, each one of us process them in a completely different way. This is so true that you can say that there's a different version of a book in each reader's mind.
So what about book trailers?
As you know, they are a kind of advertisement, but they are be quite different from their movie siblings. A book trailer should give you an idea of the story without spoil it, but it must be done without trying to show the book itself, otherwise they would only offer one version of it. And you don't know whether the potential reader would like it or not.
But truth is that many book trailers are complex, with actors and well defined settings. This choice bears the risk to influence a potential reader and not always for good. That's because it is very likely that what they see has nothing to do with what their imagination would be able to create out of the same book.
Should I be sincere, it rarely happened to me to watch a book trailer that I liked. Most of them are too long, like very short movies, which would be nice if they wouldn't be used to advertise a book.
The only ones, which I like and which are really effective in raising my curiosity in the book, are short, fast and do not show anything in particular but the idea beyond the book, which is the only part of it that all readers could see the same way.
But are book trailers really useful for advertising a book?
Well, it depends.
My opinion is that the best thing when you meet a book for the first time is that you do not know what's inside it, beside the genre. Nothing can make you more curious than a captivating cover, an effective title, maybe with a cool tag line. The blurb helps, too, but it should give you a general idea of the story, without providing too many details.
Therefore any kind of advertisement, including book trailers, should just highlight these aspects and let us fancy about all the rest, in a way that makes us be so curious and strongly desire to get that book.
Anything else is superfluous, misleading and potentially counterproductive.

What about you? Do you like book trailers? Has it ever happened to you to buy a book after watching a book trailer?