Trash Trailers?

I often wonder how effective book trailers are, and whether they’re worth the time it takes to make them.

Does anyone watch them? How would anyone discover a book trailer unless it depicted a book by a favourite author, in which case readers would probably know about the book anyway, if they hadn’t already bought it?

And does anyone actually rush out and buy a book because somehow they stumbled upon its trailer?

Writing about White Head Island (‘Island Eden’) a couple of weeks ago reminded me of the trailer I put together for Defiant Island (DreamCatcher Publishing 2007), which – self-indulgently (sorry) – I can’t resist linking here.