I'm heading out to Bozeman, MT to participate in BackpackingLight's Wilderness Trekking III in October.
As an upshot, this trip will be one of my most extreme excursions to date, likely second only to the Hudson Bay Expedition of 2005. Prior years' WT3 trips support this statement. Last year, the hikers were met with harsh winter conditions and had to hike out because of the deteriorating weather. In 2007, gear was pushed to the extreme. Two pairs of trekking poles suffered catastrophic failure. Their trip report is here. In short, the group faces snow, near-freezing temps and difficult navigation for the entire trek.
Although gear requirements have not been released, in prior years, insulation has been all synthetic. This means insulated parkas and pants, along with sleeping bags or quilts. Other gear is specifically limited. The 2007 report gear report has a prior example list. Chris Wallace has also posted his 2008 WT3 gear list.
More information will be posted as I receive it.