whew - and more than you EVER wanted to know -
Both FOR and AGAINST
The article can be found at this link:
http://www.trucktires.com/us_eng/library/publications/periodicals/RealAnswers/03v8iss3/ra8.asp
Some more links:
http://auto.howstuffworks.com/question594.htm
http://www.toyo.com.au/tech_info11.html
http://www.mtdealer.com/t_inside.cfm?action=art_det&storyID=1207
http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=6,470,923.WKU.&OS=PN/6,470,923&RS=PN/6,470,923
http://www.tirelast.com/id5.html
http://www.prairiebizmag.com/article.asp?id=401
Your question has prompted me to search for a scientific explanation.
http://wine1.sb.fsu.edu/chm1045/notes/Gases/Diffuse/Gases09.htm
"The effusion rate, r, has been found to be inversely proportional to the square root of its molar mass and a lighter gas will effuse more rapidly than a heavy gas."
We know the molar mass for N2, air and O2 are 28, 29 and 32 respectively. So, N2 should actually effuse faster than air and O2.
http://www.trailerlife.com/cforum/index.cfm/fuseaction/thread/tid/14253029/gotomsg/14254472.cfm#14254472
"According to van der Waals equation for the behavior of non-ideal gasses, the a constant for N2 is 1.39 vs. 1.37 for N2/O2 mix (standard air). The b constant shows even less of a variation: 0.0391 for N2 vs. 0.0.0342 for the mix. It should be noted that the terms are both linear in the equation.
Also, plotting the PV/RT vs. pressure for 1 mole of gas shows that one must be in the pressure ranges of 100 atmospheres before appreciable differences in expansion behavior are noticed.
Given this, one would have to dismiss the arguments provided above, except perhaps the oxidizing effect provided by O2."
Some more opinions:
http://www.cartalk.com/content/columns/Archive/1997/September/05.html
"Their claim that nitrogen keeps your tire pressure more constant is actually correct. But their reasoning is wacko. It has nothing to do with diffusion of air through the rubber.
Seriously, you can keep your tire pressure constant enough for street and highway driving by simply checking it periodically."
http://www.trailerlife.com/cforum/index.cfm/fuseaction/thread/tid/14314827/srt/pa/pging/1/page/2.cfm
"Local tire store charges $6 a tire to fill with Nitrogen. Tech I know get a laugh every time someone goes for it. Says it the easiest money the store makes."
http://www.trailerlife.com/cforum/index.cfm/fuseaction/thread/tid/14397986/srt/pa/pging/1/page/2.cfm
"Unless you are racing, Nitrogen is just another scam. Industry site shows that a dealer must inflate approx. 100 tires a month to make the units pay for themselves.... read: sales pitch."