I've had my HMG Porter for about a year now and used it on 7 or 8 trips ranging from 1 to 3 nights each. A lot of these trips involved bushwhacking through scratchy, nasty chapparal or brushing up against rock walls and boulders.
Overall I'm still very happy with the pack and the way it's help up (especially considering I've worn a hole in ULA pack fabric on similar style trips).
Obviously with the white fabric color on the HMG packs, I've picked up a lot of dirt and grime. Much of the pack is faintly stained with various shades of dirt, mud, soot and vegetation.
Around the top opening of the pack, the cuben body material has acquired a lot of wrinkles and seems like it may have softened up a little. No signs of failure or critical degradation, just looks a little more worn in this area… presumably from all the folding and unfolding when opening and closing the pack.
The bottom of the pack is pretty scuffed up. There's areas where the pack fabric is a little fuzzy from the scuffing, but that's it. It doesn't appear to affect the pack material's performance yet.
Early on with the pack, I thought I had noticed a section of stitching along a seam starting to ever so slightly pull apart. The seam in question is the one that joins the side panel and the back panel and the area where the stitching looked like it was getting stressed was in between the point where the top of the shoulder straps attach to the back panel and the uppermost side compression strap. I thought maybe the shoulder strap and compression strap were pulling too hard in opposite directions. I've been monitoring the seam since I noticed it however and it hasn't appeared to get any worse.
Overall I've been impressed with the pack's ability to withstand some nasty brush. I also am really liking the variable volume of the pack (thanks to the compression straps and huge extension collar) and the modularity afforded by the abundant daisy chains. I've got all sorts of ways of attaching various pockets and/or equipment/tools and can customize this to suit my needs for each trip. I find the pack super comfortable at 35 lbs or less and with careful packing have been able to creep up above 40 lbs when hauling lots of water, etc. with comfort.