I also purchased this bag about 6 months ago, specifically to use on carry-on-only trips.
I have used it on 4 3-day weekend scout trips abroad, with uniforms, full waterproofs, spare shoes/boots, and clean clothes for the trip home. I guess a weekend of camping takes about the same amount of gear for me as a 5-7 day trip to the city.
A few times I've used it as carry-on, with a regular suitcase checked in - I easily packed emergency spare clothing, toiletries, 15" laptop with charger, DSLR with extra lens in camerabag, waterproof jacket and various small bits and pieces, and it still compressed down to way smaller than the roll-aboards lots of other people were using.
I do love the bag. It JUST sneaks in under measurements (for most European airlines, at least), and one of my most used airlines have no weight restriction on handluggage. The other thankfully does not normally weigh, as long as you look like the bag weighs nothing - and the porter makes that pretty easy.
I do use the second set of female connectors for the buckles most of the time, I find them easy enough to get to. The top pocket is just for travel papers, liquids bag and stuff I immediately need. Definitely, stuffing this pocket puts you at very high risk of exceeding bag-height on European airlines, just saying.
It was on this forum that I first read about the Porter 46. I already had another Osprey hiking backpack, and I am totally pleased about my decision to get the Porter 46 (I got mine at REI while on vacation in the US, I've not seen them in Europe).