In reply to tehmarks:
I've a pair of the stretch Brions which are basically the Zions without a pocket or vented crotch.
Really nice fitting and comfy trousers but they wore a hole in the knee my first time climbing in them. I don't recall any aggressive or unusual knee rubbing, scraping, banging or dragging so was a little perplexed as they're advertised as "abrasion resistant" hiking/climbing trousers.
I contacted Prana who basically told me "they can wear out with abrasion" - hardly abrasion resistant then - no offer of repair or replacement and told me I should buy some other model of their trousers instead that have thicker material.
Shame as I like the feel and fit but I've chalked it to an expensive mistake and will send my money elsewhere in future.