So I've had the Miura all summer, and I've taken it bouldering, car-camping, hiking, and even used it simply to transport my clothes when visiting my parents.
The bag is marketed as a climbing pack for transporting all your gear to the crag. There are gear loops inside for clipping all manner of business to, and the bottom is shaped to perfectly fit the Arc'teryx rope bag, the Pali. It fits my own, much less cool rope bag too, if i take more care in packing. The main selling feature of the bag is the fact that - by way of two full-length zippers - the front flips open completely to reveal the contents.
OK. The roll-top closure on the bag is different and takes a little getting used to. Once I had it, though, it was great and allowed for a super-fast pack/unpack. The flip-down front was an amazing feature that made organising a breeze because I could access everything I put into the bag at once, no digging required. I absolutely love this feature and would definitely like to see it on other bags. That being said, this bag is more for folders, not so much stuffers. Even with the side zippers done up, the stiff edges of the roll-top make stuffing a little hard.
The nature of the roll-top also means that if you ride a bike with this bag, unless it is a relaxed cruiser bike, the top of the bag will press into your head. If you wear a helmet, definitely don't wear this bag because it'll just be too hard and annoying to properly see the road.
The zippers and not at all waterproof, and although the face fabric is a little water repellant, the bag is definitely not made for rain. The bottom of the main compartment is coated on the inside (probably with polyurethane) for durability and waterproofing...the catch is that if water gets IN, it just pools on the bottom.
The Miura has the outstanding quality of construction you would expect with an Arc'teryx product and excellent attention to detail. The pack is comfortable to wear and an easy-carry for hiking with. I would say that day trips and weekends should be a breeze, and you would love the flip-open feature for these shorter trips. For longer excursions though, or heavier loads, a dedicated trekking/backpacking pack would definitely serve you better.
All-in-all, the Miura is a wicked cragging bag and the 30L version would make a seriously pimp (though pricey) day-to-day bag for doing anything. The flip-down front is a delicious feature that you will definitely come to love. The cons I listed above are mainly due to me using it for things it wasn't really designed for, though the water resistance is something I would still gripe about.
Arc'teryx Miura 50, I give you 8 locking 'biners out of 10.