Nitrogen is great for shocks, not cheap enough yet for my tires. Plus if you ever get low, you can't just grab the air hose and fill.
Nitrogen fill is one of those things like dynabeads or centramatics, spend your money on something that takes the hastle out of you maintaining your bike. Or replaces something that is most of the time done for free, like balancing your tires.
Nitrogen is suppose to respond less to temperature changes i.e, it will cause you to not check your tire pressure that often because why class? The nitrogen is less susceptible to pressure change based on temp, or so the guy tells you thats charging you to fill your tires. Something the guys on Goldwings have done because they can't find anything else to spend their money on.