yeah I looked into this (via forums and my own research), but regular tire air (aka oxygen) is ~80% nitrogen anyways.
unless you track your car, or putting it in storage for a long period of time etc, then its a waste of $$
I mentioned storage b/c regular air isn't as compressed as much as nitrogen is and therefore has the potential to carry more moisture which can lead to inner tire rot over very, long, extended periods of time. Nitrogen is essential "dry" air. But modern tires are pretty durable these days anyways...
don't let the dealerships sucker you into putting nitrogen into you tires saying it will hold pressure better. It does, but by a margin, and for most of us that are daily drivers, really not worth it. Just maintain proper tire pressure with regular air and you'll be fine. If you're a track rat, then i'd say yes, do it.
just my .02 cents.
and here is a thread of where i'm coming from: