Good interesting topic. We use Jack-knife push-ups on rings pretty frequently. Looks a hell of a lot like a triceps extension although there is a potent core involvement. I know without a doubt it improves everything from muscle ups to handstand push-ups. The Westside PL'er, as Steve points out, swear by big volume triceps extensions. There are also loads of PL'ers who do nothing but the 3 lifts. We have people at the top of the game using fairly different approaches, that's pretty interesting to me. I'm not sure what conclusions to draw but it's interesting.
I think I saw something form Kelly Baggett:
that said something to the effect "one has a limited growth/developmental potential using isolation movements. The addition of full body movements produces a greater neuroendocrine response which can actually create a more anabolic environment for the isolation movements to produce further progress..." I think that was from an article on that site...if I flubbed that, my apologies.
I think for basic time efficiency isolation movements to not hold up well in a training/coaching situation. As much as I like Jackknife pushups I can get so much more work done with dips, ring dips and the like. Jackknifes do make a nice finisher however...
Personally I would not approach isolation movements as a complete no-mans land but its rare that I find much need for them.