I have taken this pack to Havasu Falls last year and I loved it. Although it's not as comfortable as TNF Catalyst 75 (heavier), It was good enough for me carrying about 45 pounds of gear for over 10 miles.
Personally I think 70 liters is the best size backpack if your budget calls for only one pack. I've tried 55 liters, but it seemed a little too small even for a weekender and I am not even one of those "pack everything but the kitchen sink" type of a guy.
I've also used Naos on a canoe trip and it worked well since it's waterproof.
I've taken it into airplanes without the hip belt since it fits into the overhead compartment (barely :).
Bombproof pack! Super strong! A pack that Superman would carry!

I know it's expensive, but this pack will last you decades if you take good care of it.

This is an awesome pack. My new favorite. It is waterproof and it has a roll-top like a dry bag. It is very well made.

I think I was one of the last holdouts in the world on my external frame pack. I loved the rigidity of the frame and the ability to tie things to the frame. When I finally bought an internal frame pack I knew it had to be a good one. When I saw that this one was water proof and had the disc system for weight dispersment I bought it. I no longer get the aches in my joints that I used to and the pack very waterproof. Only thing I will say negative is that there is not much air ventilation to your back. Overall this is worth the money!

Within months I tried a lot of different backpacks but fell in love with the Naos. When the '07 model went half-price I had to invest the money. It is the first 'expensive' backpack I owned and ever since, all my friend's backpacks feel saggy and uncomfortable on my back. It is true, the packing needs consideration and good planning, but I think this is always important when going into the outdoors. I only encountered medium rain with the pack. BUT: when hiking in lots of sand and dust recently i realized, waterproof means dust-proof and even insect-proof too. my gear stayed perfectly dry and clean. /// Once i carried 15 Kilos (33 lb) with my backpack and surprisingly long it felt comfortable. I don't have a hyper-strong back but could handle the weight well.

In Switzerland one hiker called my Naos the 'Porsche' of the trekking-packs. I started to believe him already.
If you consider this extraordinary backpack, be sure to get it on your back first, loaded with i.e. sandbags to simulate the trekking-feel. If it feels right, I can highly recommend buying it.

Expensive? Yeah, but this is an investment you cannot afford to miss out on. Arcteryx packs are rivaled by no one when it comes to comfort and suspension. The pack itself does run a little heavier than other packs --- but the suspension makes it a moot point. You do not fatigue from a poor fitting pack or a load that transfers all over your torso.... I've had that happen with other packs. You'll need to get used to a top loader if you have not used one -- but they force you to simplify and put thought into the way you pack. This pack is an all around winner. You cannot lose with it. It will run you some dough --- but you should have it forever.

I was fortunate enough to find an Arcteryx Naos 70 on steepandcheap.com last year. It is a fantastic pack. Everything they say about the waterproof fabric is true - you can dunk it under water or float it down a river and everything in the pack will remain dry. The best thing about the fabric in addition to its waterproofness is its durability. It is definitely not going to tear when rubbed against a rock or when passing under a down tree.

The pack is however too heavy for my tastes, so I am going to switch to one of the smaller Acrux packs, but other than that I have nothing bad to say about the Naos.

I love this pack so much. It feels so comfortable to wear. There's so much area to pack as much as you want. With practically no restrictions on packing, save what you can actually lift, it really affords one plenty of backpacking options. For me, it's mountaineering. Here, there's ice ax loops on the back. I love the pack's red color, which will stand out easily on a snow-white mountain.