I am still trying to understand what are intensive and extensive properties. Possibly someone can give a pointer to a decent text (preferably on the web), as I am not too happy (to say the least) with what I found so far on the web. I already asked here one question on this, which I finally answered myself.
My new problem (among several others) is that density seems to be one of the first properties taken as example of an intensive property. While it seems a good approximation of what I know about solids and liquids, it seems to me a lot more problematic with gas, as they tend to occupy all the available space you give them.
But none of the documents I found seems to make any resriction regarding density of gas. It seems to me that my opinion (apparently contested) that velocity is an intensive property, may be easier to support than the intensiveness of density in the case of gas. Or to put it differently, I do not see why pressure should be more intensive than volume, while wikipedia lists pressure as intensive, but not volume. Ideal gas law states that $PV=nRT$, which apparently gives a pretty symmetrical role to $P$ and $V$. And density depends on pressure (actually using this same formula and molecular weight).
If it were not for the fact that some principles seem to be based on the concept, such as the state postulate which I found on wikipedia, I would start wondering whether these are real concept in physics.