A lot of the guys over on Jims are starting to use these plastic firkins, the smaller craft breweries are also using them, I would not worry about oxygen permeability, it doesn't seem to bother the pros.
The brown 4.5 gallon pin is quite a popular one that I see a lot of the lads using.
<edit> the pins not a cornie alternative as they are casks for cask ale. The other kegs would mostly be just that, kegs and you'd need a pub system for dispensing, I'm not sure how much of the cornie gear would be reusable.