Got tires filled with Nitrogen. It's living up to its promise of better ride and lower heat build-up. There goes free air. Marketing geniuses have found a way to earn money on 'gas'. Rs 100 for 3 months checking of air/nitrogen.
Further to more than 2 months of Nitrogen checking, I searched online for reactions and experiences and encountered this interesting report: http://blogs.consumerreports.org/cars/2007/10/nitrogen-tires-.html