I race circle track cars and we use Nitrogen to fill all the tires. It is more stable than compressed air because it has less or no water and other impurities in it. You can get a cylinder at any welding supply store for about $35.00 plus the cylinder rent. A large cylinder will fill your four tires and about 120 more.....
To make it even worth while you have to purge your tires to get all the ambient air out of them. If you don't there is no benefit because the little amount of air left over has water in it thus negating the positives nitrogen fill gives you.
We use a vaccuum pump to completly deflate the tires and refill with Nitrogen. This is expensive and hard to get....The easier way to do it is to let the ambient air out of the tire by pulling the valve stem. Inflate the tire with nitrogen and let almost all of the nitrogen out of the tire. If you let it all out, then ambient air will be sucked back into the tire and you get no benefit. Repeat this process about three times per tire. Then you should have 99% nitrogen in the tire.
What does it do??? It helps maintain more equal tire pressures over a wider range of temps and elevations.
Did I do it? Yea, I have 3 Nitrogen cylinders sitting arround because of my racing and I get bored.
Would I do it if I had to go out and buy the Nitrogen???? Nope.