When I was reading Laura's post about running and being in the zone I remembered this wikipedia page that I had come across one day that talks about something like that. There is a Hungarian Psychologist who has studied this, in what he calls, the Positive Psychology Concept. He also has a very hard name to pronouce, Mihály Csíkszentmihályi, here it is phonetically if you want to try: mee-hy cheek-sent-mə-hy-ee
To continue, in this article he describes the state of being in the zone with the words "flow" ; He defines "flow" as completely focused motivation.
Csíkszentmihályi in an interview said that flow is, "being completely involved in an activity for its own sake. The ego falls away. Time flies. Every action, movement, and thought follows inevitably from the previous one, like playing jazz. Your whole being is involved, and you're using your skills to the utmost."
When immersed in a state of flow, it is theorized that conditions that are called temporal concerns are no longer present, for example (food, sleep, ego-self...)

According to Csíkszentmihályi these three conditions are necessary in order to achieve flow.
Also Csíkszentmihályi gives an example of ten associated conditions that one may experience during a state of flow
Conditions for Flow

1. One must be involved in an activity with a clear set of goals. This adds direction and structure to the task.
2. One must have a good balance between the perceived challenges of the task at hand and his or her own perceived skills. One must have confidence that he or she is capable to do the task at hand.
3. The task at hand must have clear and immediate feedback. This helps the person negotiate any changing demands and allows him or her to adjust his or her performance to maintain the flow state.

Components of Flow

1. Clear goals (expectations and rules are discernible and goals are attainable and align appropriately with one's skill set and abilities). Moreover, the challenge level and skill level should both be high.
2. Concentrating, a high degree of concentration on a limited field of attention (a person engaged in the activity will have the opportunity to focus and to delve deeply into it).
3. A loss of the feeling of self-consciousness the merging of action and awareness.
   
4. Distorted sense of time, one's subjective experience of time is altered.
5. Direct and immediate feedback (successes and failures in the course of the activity are apparent, so that behavior can be adjusted as needed).
6. Balance between ability level and challenge (the activity is neither too easy nor too difficult).
7. A sense of personal control over the situation or activity.
8. The activity is intrinsically rewarding, so there is an effortlessness of action.
9. A lack of awareness of bodily needs (to the extent that one can reach a point of great hunger or fatigue without realizing it)
10. Absorption into the activity, narrowing of the focus of awareness down to the activity itself, action awareness merging.

Not all are needed for flow to be experienced.

These are the two Wikipedia pages I summarized from that talk about this if you want to read more:

1) http://en.wikipedia.org/wiki/Mihaly_Csikszentmihalyi#cite_note-7

2) http://en.wikipedia.org/wiki/Flow_%28psychology%29