I gotta say, I'm pretty surprised at this thread. I think nitrogen is absolutely worth the cost for an autocross or track car. For a daily-driver-only, yes, it's marketing BS (especially about it not leaking out as fast -- wtf?).
Running nitrogen for the past couple years, I have learned that it saves me from having to bleed during a heat and re-add air after the event. Nitrogen does expand when hot, but not nearly as much as air does (and yes, I am aware it's not pure nitrogen,

point still applies). If I have my tires set to 32psi cold, then on a hot July autocross day and the car is sitting in the sun on hot tarmac the pressures would get up to 42-45psi after a run or two. This makes the car feel like it's skating and I have to let air out to achieve the appropriate pressure for good grip. But then when I get home and drive to work the next day, they only have ~27psi in them, and I'm not getting optimal fuel economy and I have to add more air to get them back to where they need to be for daily driving (or the next event in colder temperatures).
With nitrogen, however, I can have them set to 32psi and even on the hottest autocross days the highest I have ever seen is 35-36psi, and this is perfectly acceptable for good grip in my car on hot tires. At the end of the event, I drive home and the next morning they're back at 32psi and I'm good for daily driving.
Maybe I'm lazy, but one extra thing I have to do during and after an autocross is not something I really want to do if I can easily avoid it.
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2015-2017 President
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2002 Subaru WRX [dd]
2002 Honda S2000 STR #3 (retired...for now)
1992 Acura Integra ChumpCar #118 (retired)
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