@ Dave, I agree with Rob, unless you do a controlled experiment, it means nothing.
I have a similar stance to Rob, I don't really care if people use it or not in their tyres and on face value it would seem to make no difference (negatively or positively). I might use it if it were free, but it wouldn't swing me to go to one supplier over another because they had it for free or at a cost. But I do like people to have the correct info though and not be hoodwinked into a trend or gimmick that is claiming to do something it is not.
While searching the web lastnight about it, I did find some discussion going on about a test that was done comparing the deflation rate of a tyre filled with pure N2 rather than freshair (it didn't mention if it was dryed to this could've been a factor in the results). It seemed that after inflation to 35psi, and left for one year, then rechecking that the N2 tyre had lost 2psi, the air tyre had lost 3.5psi. This seemed fairly consitent across the tests. The conclusion was that given regular vehicle maintenance (i.e. checking tyre pressures regularly) it gave no appreciable gain in holding its inflation. However, it does tend to suggest that although logically/scientifically there may be nothing to support the fact that N2 lost less pressure, that in the real world it did indeed seem to hold some truth.