When I bought my brand new PowerBook G4 17" in 2004, I splurged and bought a Brenthaven backpack for it. Back then it cost a good deal more than the usual backpack -- around $75 -- but I thought it would be worth it since I lugged around my PowerBook nearly every day and it looked like the Brenthaven provided better padding than the competition.
Since then, the backpack has housed a succession of three 17" PowerBooks and MacBook Pros under very heavy use. The amazing part is that outside of being a bit dusty, it's in just as good shape as the day I bought it. No frayed stitching, no stuck zippers, no torn dividers. There is no sign of wear and/or tear whatsoever. And if there was, or ever will be, all Brenthaven bags come with a lifetime warranty.