I've had the opportunity to use the Platypus Pack for several mountain bike trips and have been very pleased. One of the best features is that the main compartment is waterproof. I've been on a couple of rides where I got into a small microburst and all of the contents in my pack (including my iPhone) was perfectly dry. I also really like that when I fill my reservoir I don't worry about it being wet and getting everything else in my pack wet. This is due to the fully waterproofed-taped main pocket. I also love that it doesn't become a round tube when I fill the reservoir full (often happened with Camelbak). It sits fully flat on my back and is super comfortable. I haven't experienced any wear issues up to this point. It has been a solid pack and looks great as well.
I also really love that I don't taste any plastic when drinking from the reservoir. This has been a major complaint from all of my Brand X toting friends, even those with their latest reservoir. It is the only one that I've found that doesn't have that plastic taste.
All in all a very nice, well-thoughtout pack. I highly recommend it...