Its been a habbit now for me for about last 10 years. And it is a good thing believe me. It helps in reducing load on starter self, helps battery life, cleaner cumbustion chamber, lessen the need for car tuning, lessen the chance of fuel pump mal-functioning, keeps engine load lesser on cold start ups etc.
I usually do this also when I park my car in office, when I know it will not be started again for the day or more than 4 hours.
And also I usually shift to CNG on third gear, so it absolutely give me no hassles in shifting.
At an idea, I consume about 1000 rupees Petrol per month due to this habbit on an average of around Rs.5000's CNG consumption. This also includes casual driving on Petrol once a week. I have learnt that this keep car in good health overall.
Current rise in CNG prices, Rs.60 per kg, will effect about rupees 1K per month to me. 