Well, the first thing I'm going to use it for, I think will be for the floor of a inner net / bug tent for my myog two person 'mid shelter that is currently under construction.
I know a lot of people use silnyon for tent floors, but I hear all over that it seeps water, eventually gets holes in it and just wears out. Tyvek is commonly used as a ground cloth, so it just got me thinking. I could just make the floor out of something cheap, and when it wears out, it wouldn't be much of a deal to rip it out and sew in a new one.... And beyond that, I just started getting curious about how it's properties compare to other common materials. If I recall, I think the Tarptent folks even offered a shelter made from tyvek at one time...
And that is a pretty attractive pack. Seems like tyvek would be a great prototyping material.