Rating: 4 / 5
Update: 9 May 2007
Sierra Designs evaluated and replaced the jacket. Their customer service was exceptional and incredibly responsive. I will continue to evaluate the performance and post any new findings.
Update: 21 April 2007
Sierra Designs customer service responded to my inquiry, saying: "We do not usually see any major damage happening after just one use, and so it may be a flaw in the coating." They have offered to evaluate and repair/replace the jacket. If this proves not to be a systemic problem, the jacket could easily be rated a "5" for its weight/performance ratio.
Used the Isotope Jacket continuously for two wet, cold, rainy nine hour days on the Superior Hiking Trail near the MN/Canada border between 31 March and 1 April 2007. It was exceptionally waterproof under all conditions, including downpour, and very comfortable fully zipped and cinched in the 35-45F temperature range at moderate exertion (~3mi/hour). High exertion such as climbing steep hills or long staircases required a few minutes of ventilation with the front zipper.
I wore the Isotope (Men's M, 5.0oz) layered over a Smartwool Microweight Crew (M, 6.2oz) and GoLite Kinetic Jacket (M, 14oz). No noticeable moisture buildup occurred over the two days, despite being unable to dry gear due to weather.
One problem was noted with the interior liner in areas of increased friction--notably the mid-back and shoulders--from my pack (17.23lbs with seven days of food, trip cut short due to injury):
Right anterior shoulder
This jacket was purchased new two weeks before the trip with no visible wear. I have contacted the manufacturer for comment.
Overall I was very impressed with the performance of this jacket, and sections with visible wear do not seem to impair performance. I rated it as a "4" due to the visible wear patterns appearing after only two days of use.