But one example is often markets where user behavior is fundamentally shifting, or where there is a sudden change (e.g. adoption of truly smart phones) leading to opportunity.
Great point. A very good write-up on that is http://jasonlbaptiste.com/featured-articles/build-what-had-p....
Maybe I will write a post on how to identify a great market, as that is a pretty big topic.
For what it's worth, I'd love to see you write that.