I have done a lot of building and even more "fixing" of old crap lines. I have also done a lot of coordinating of groups for trail work. I know Mark and I have attended an IMBA clinic. He helped design one of the trails we built in our area.
In my opinion, any trail or section of trail that is "built in a day" is somewhat doomed. I say that because in my experience, unless you know what the weather and conditions are like in an area over a period of time, you won't know what the best solution is for a section of trail. What might be a great solution in a dry area with low traffic might be total crap if that area gets wet and sees high traffic.
The projects that have turned out like crap that I have been involved were ones that we showed up on the day with a bunch of people, tried to figure out what to do and went at it for 3 hours and finished up.
The better ones were visited by the crew bosses before hand, the work was planned in line with conditions (weather, traffic, line etc.), an appropriate solution was settled on, materials and tools were set up, THEN the work got done. The results after a process like that have left us with what I would call "sustainable" trail.
As an outsider to this event what I see went wrong was that the people "in the know" weren't consulted, so the best solution wasn't applied and possibly a "solution" applied that didn't even need to be there.
I also think this thread can have some positive value. The Mtb community needs an outlet to discuss what is happening and if something isn't working we should discuss it. Yeah it might bring out some negative opinions, but those might lead to some positive change. If you are too scared that outsiders will see us having a discussion about how a trail was built then too bad. What I see is IMBA being held accountable to a high standard of building and I don't see anything bad coming out of that as long as reasons are given. Good trail says far more about our sport than some negative opinionson the Internets.
My approach is that IMBA and Whistler provide guidelines and principals on how to build trails. But you also need to take in to account local knowledge and adjust accordingly.
Once I learned what I would call mtb trail building basics the book Natural Surface Trails by Design was one that really made me think about all the factors that go in to making a line choice and the consequences of it. It really helped me look at trailbuilding in a different light.
I also know that one of the challenges IMBA faces is funding. They moved in to paid consulting for trail building because they needed an outside income source, but more importantly, they do have some extremely knowledgable people on how to mtb trails. Those people also know how to translate that in advocacy as well. They should capitalize on it as the overall result is a benefit to the sport overall.