Okay, I know I'm late to this one. It was covered by Exbeliever and God is for Suckers! a week ago. Part of my excuse is that I can only take presuppositionalism in small doses.
The event is the Barker-Manata debate, available as a podcast from The Infidel Guy. It's currently the third one down. The topic is "Which is More Rational: Christian Theism or Atheism?" with Barker representing the atheist side and Manata representing the Christian side.
Manata started off with a presuppositionalist strategy. As presented by Manata, it works something like this: if he and Barker attacked eachother from the point of view of their respective worldviews, they'd be begging the question. Therefore, they had to provide "internal critiques," basically finding inconsistencies in eachother's positions. Manata then provided a ton of quotes from Barker's book Losing Faith in Faith to show that Barker conceeded Manata's views were internally consistent and Barker was not consistent. It's an incredibly unusual and pedantic way to debate. I have difficulty seeing how it could appeal to any Christian not steeped in presuppositionalist apologetics. At the time, I thought Manata's only hope of coming off looking good was to mix his rather odd arguments with some melodramatic preaching.
The main thing I remember from Barker's opening statement is his argument "You can presuppose anything and have it be internally consistent. You can presuppose that the world was formed by ducks bringing up dirt from the bottom of a lake."
After opening statements was cross examination. Manata spent his time trying to catch Barker in trivial contradictions. Barker's segment was hilarious. He raised the simplest of evidential challenges to Christianity, using comparative mythology and the point that the Bible features talking animals, but we don't see talking animals today. Rather than try to meet these points head on, Manata kept insisting that any attempt to evaluate Christianity with evidence begged the question against Christianity.
Manata's rebuttal was more of the same, harping on alleged contradictions. Barker spent most of his time trying to answer these, a mistake, I think. He should have structured his rebuttal like this: "On the face of it, it seems we should evaluate theism the way we do other claims about the world. That means looking at the evidence. Manata has failed to show otherwise for reasons X, Y, and Z. I have provided evidence against Christianity, and Manata has not produced a shred of evidence for it." I think that is the proper way to debate presuppositionalists. Barker instead got sucked into Manata's bizzare presuppositionalist methodology.
In the concluding statements, Manata got going on the preaching. He linked alleged inconsistencies to sin, and declared that his Lord is the "Lord of Reason." That last bit cracked me up.