It's well thought out, doesn't have any useless bells…
Design: front loader
Number of Pockets: 2
Max. Load Carried: 14lbs+
Height of Owner: 5'9"
Price Paid: $69.99
It's well thought out, doesn't have any useless bells and whistles, and feels great on your back. I'd compare the overall quality of this pack to Arc'Teryx. The main compartment is generously sized and can hold a more than enough gear and supplies for a full day on the trails. The outer pocket w/waterproof zipper is large enough to hold an insulated jacket and pants.
Now for the problems. The hydration tube port is too small to pass a hose through without removing the bite valve. Fortunately this is easily fixed with a careful snip of some scissors or cut with a razor blade. Since the hydration port is made of neoprene it won't unravel if it's "widened".
But the BIG problem with this pack, at least with the 20 liter version (has "20L" embroidered on the right side) is the loud squeaking that comes from the sternum strap attachment with every step the wearer takes. The squeak is caused by friction between the plastic tubes which the sternum straps connect to. This tube is sewn into a nylon sheath on the inside of each shoulder strap, and the sternum straps connect to this, allowing the sternum strap to slide up and down to adjust the placement of the strap. Apparently the tubes are made out of something that produces slight friction against the enclosing sheath, and produces a loud squeak when the shoulder strap moves even slightly. I should note here this type of squeak has plagued several different manufacturers over the last several years. Most notable was Osprey, with the early versions of their Aether 60 model backpack, known in climbing and backpacking circles as the "squeaky" ones (versions made prior to 2003). The simple fix Osprey chose was to change the type of nylon that came in contact with the rods, this eliminated the friction causing the squeak. And that's probably the same fix that would work with the Sidewinder, but more unfortunately, Black Diamond chose instead to discontinue the 20L version of the Sidewinder in favor of a 30L version, which is probably more capacity than most people need in a daypack unless they're carrying climbing gear or other heavy, bulky items.
The last problem is the meager 1-year warranty Black Diamond offers on their equipment. Most other companies making premium-quality outdoor equipment offer lifetime warranties against manufacturing defects, BD can hardly excuse itself simply because they manufacture equipment targeted for climbers, who would supposedly put heavy wear on their gear. BD has moved into the hiking and backpacking niche with several lines of gear, and should modify their warranty on these items appropriately.
For this reason I'd recommend against buying any BD gear specifically for use hiking or backpacking, there's a larger selection and better product support from other manufacturers.