Usually I don't decide things on the spot (unless it's something rather minor or I'm actually forced to), but sometimes...
I just saw a trailer for the new Tim Burton/Johnny Depp movie, "Sweeney Todd", and decided, immediately as it is, to watch this movie as soon as it is out in Germany. Mad, I know (though probably not as mad as Sweeney, judging from the trailer).
I can't really say what it was that made me decide this on the spot. Several factors, would be my guess. There were the main actors I saw so far - Johnny Depp and Helena Bonham Carter, both of which I like. There was the look - a "typical" Tim Burton movie (and I love these). There was the idea of coupling an old-fashioned killer (and killing with an old-fashioned razor makes you old-fashioned in my book) with an actual musical. And, I admit, the scenes shown during the trailer had something to do with it as well. All together somehow touched me, made me want to see the whole picture. On the other hand, that's what trailers are for, isn't it?
So I'm looking out for Sweeney and hoping the movie will run in the movie theatre in my hometown.