In the discussion on the site, it was pointed out and confirmed by Marshall that the glass carboy was a 6.5G and the PET was a 6G. So there may also be some headspace/geometry things there that could explain the differences in observed foam. The surface texture and adsorption stuff also seems quite plausible.
I agree that oxygen at such a small level over that timeframe seems highly unlikely to cause a noticeable difference, but our bodies are amazingly sensitive instruments. It's reading the gauges that's the hard part
![Wink ;)](http://www.homebrewersassociation.org/forum/Smileys/default/wink.gif)
One other thought -- if PET is oxygen permeable to some small degree then doesn't that mean CO2 also escapes to some degree? Again, I'm skeptical that this is enough to make a big difference over such a small timeframe, but curious if anyone has thoughts on what that actually looks like from a feasibility standpoint. I don't know the right formulas to even begin to approach that mathematically.