Compressed air is 78% Nitrogen, 21% Oxygen and 1% other gases; so using compressed air is pretty close to full Nitrogen anyway. The Nitrogen molecule is bigger than the Oxygen molecule and will not seep out through the tire as quickly, is more stable over a wider temperature range than Oxygen (about 1 PSI over 10 degrees); the BIG reason though is that Nitrogen from a cylinder is DRY. It is the moisture in the compressed air that causes so much havoc. Water vapor that condenses, evaporates and maybe freezes inside the tire causes all kinds of bad things; bio growth, wildly fluctuating pressures and tire breakdown are just the biggest concerns.
There is nothing wrong with using old fashioned compressed air in modern tires, the drier it is the better obviously. Racing tires don't use just Nitrogen but a specialty mix of gasses primarily Nitrogen and Oxygen in specific ratios to keep gases from migrating, look up Dalton's Law of Partial Pressures for more on why this happens. However, they run on the ragged edge of performance where it makes a difference; at those pressures, temperatures and speeds it makes a difference, for most of us it just means less pressure checking.
So if you need to add air to your tires go ahead, and try to use the driest compressed air you can.
Here's a cool thing to consider tho: If you add 100% Nitrogen to your tires eventually the mixture of gasses will equal the ratio of atmospheric gasses, that is 78% N2, 21% O2 and 1% Other gasses. Even though Nitrogen will not migrate OUT of the tire, other gases will migrate into the tire causing a rise in pressure, maybe not measurable with a tire gauge, but it will be there none-the-less. Dalton's Law of Partial Pressure at work...
Sorry that is so long winded, but my job involves working with gasses...