Biodiesel from waste oils is what I would call an 'opportunistic fuel' in that it's really only a 'for the individual', locally source, short term alternative- it really isn't scalable to a degree that would offset significant usage of fossil fuels, let alone be noteworthy of any importance looking to the future, or to big business for the mater - the most likely reason you don't hear much about it.

Scalability is often something that people forget (or ignore), for example tallow... sure you can get your B5 or maybe even B10... but what about after that? Personally (from a business perspective) I don't see the point in chasing options that can't replace a significant portion of petroleum demand.

Although in saying that, if you can do it now - yourself - go for it.

As for the corn argument, it's really only a mater of time before feedstocks switch to a cellulose based alternatives- however until an alternative arises, we will probably continue to see corn ethanol grow (although more efficiently I must say). You can't replace something with nothing, especially with half the world running around with green fingers.

Also in terms of ethanol efficiency, I suggest ethanol is on the way out too... give it a few months and we will all be talking about 'bio-gasoline' derivatives... but that's another discussion in itself...

Best,
Haylon