I like a do-it-all backpack for commuting use and for light skiing.
I want a backpack with the following features:
20-30 litres capacity
Back ventilation is a must (I sweat big time, most of the backpack I've used don't do the job quite well)
Hip belt, sternum belt.
Somewhat weather resistant, not necessary as one can use a pack cover to protect from elements.
Outboard straps for extended capacity if needed (such as strapping a spare pairs of shoe or a jacket)
Here's what I have found that match most of my criteria but missed one or two.
Marmot Zephyr, it's got everything except ski straps.
Camelbak Hellion, missing a back vent (granted, it's for winter use, but it's got the ski straps)