http://www.austega.com/education/articles/flow.htm excerpt:
In simple terms the research showed that people were generally unhappy "doing nothing", were generally happy doing things, and generally knew very little about what made them happy.
How does it feel to be in "the flow"?
* Completely involved, focused, concentrating - with this either due to innate curiosity or as the result of training
* Sense of ecstasy - of being outside everyday reality
* Great inner clarity - knowing what needs to be done and how well it is going
* Knowing the activity is doable - that the skills are adequate, and neither anxious or bored
* Sense of serenity - no worries about self, feeling of growing beyond the boundaries of ego - afterwards feeling of transcending ego in ways not thought possible
* Timeliness - thoroughly focused on present, don't notice time passing
* Intrinsic motivation - whatever produces "flow" becomes its own reward