I have made two significant changes to my 2009 Ohm. I added a mesh back panel, and I replaced the carbon fiber and Delrin rod with an aluminum one.
It is hard to avoid a sweaty back when the back of a pack is a bare waterproof panel. I added a two-piece mesh panel. This gave me a little more room inside, and allowed me to use the foam sheet as a sit pad on the trail and in camp. And it gave me a dry back.
The mesh by itself is a vast improvement. The foam sheet is a 1 ounce camp luxury.
I have never understood how a flexible hoop could effectively transfer weight to a hip belt.
I replaced it with a solid ¼" aluminum stay. Shaping the aluminum to match the radius to the hoop pocket looked like a challenge. But then I noticed the "Hydro Ports" on each corner – they were square, and right where they needed to be. So a "square cornered hoop", like a Gossamer Gear or a Six Moon Designs, came to mind. And it turns out the SMD Large was almost a match for my Medium Ohm. I needed to shorten the stays about 1.25" to get a perfect fit. The weight gain was 2.6 ounces.
This is one stiff, and comfortable, pack.
With these two mods, the hip belt pockets, a few extra straps, a watch and compass, and the dirt, the weight comes to 28 ounces. The improved performance is worth it.