I have a friend who turns his engine off at every opportunity. (Don't do this is gets really pedantic!)
The big problem is those cold morning where people leave cars ticking over on their drives. (Incidentally if it gets stolen whilst you are doing this you will not have insurance cover!)
I turn my engine off at train crossings and in traffic jams where there is little prospect of moving.
I would agree with HDI about turning off an engine before it is warm causes major problems. People frequently use a car to drive distances of less than a mile so combine the short journey with a long idle time you are looking at a recipe for disaster!
A 30 second tickover is good - it gets the oil pressure up. You should avoid pulling away immediately and allow time for the oil to circulate.
On cold mornings throw a hot water bottle in the car on the dash or steering wheel. Then pour warm (not boiling or hot) water on the screen to clear it just as you are ready to leave. (If its too hot you risk cracking the screen!
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