The ultralight backpacking community has been using Tyvek for the different uses discussed here for several years. It is commonly used as a groundcover underneith tents. There are even people making Tyvek bivys, jackets, etc.

It is breathable, but it doesn't breath fast enough to prevent sweating, but then again, neither does Gortex.

It works well for disposable weather/dirt/grim protection. In my experience it's also a bit tougher than it looks. Ever try to open one of those tyvek post office bags without a knife? It's not easy.

I use Tyvek coveralls when I'm using a paint sprayer and they hold up to several days of use. I end up throwing them away because they get gross and I don't want to deal with them anymore. I have had a few split at the seams when bending/kneeling though. When I was commuting I kept them in my car incase I needed to change a tire, etc.