eesh
Question... Are you looking at just the frame or the complete bike? If you are looking at the complete bike, the parts spec alone would make it worth it in my mind.
If you are just going frameset....That's a tough one.....
I had a carbon HT last season. I noticed stiffer bottom bracket area while pedaling, and stiffer front end. It felt like it pedaled on its own sometimes.... The vibration damping was hard to tell. It took the real high frequency stuff away a bit, but the increased stiffness made the hard hits....harder.
As far as durability, it's going to last longer (fatigue), and if properly built it will be stronger on a hard front end hit as well. The only area I had issues was with technical rock gardens. I had a couple rocks that my tire kicked up strike the chain stays on nasty steps and it tore into the carbon, whereas it would have just scraped and maybe dented in the aluminum a bit. I also had my tire kick up a big rock and hit the tube near the BB and put in a good gash. A protector behind the front wheel would add a fair amount of weight.
If I had a geared bike for training and trail rides I would have gone carbon in an instant. I would race it and ride it on less rocky rides rides. However, there are many nasty technical rides that i love to do where the HT SS just won't cut it.
I can't afford a full stable, and I know I would ruin my frame sooner or later. The Alum frame is also cheap enough that I can e-bay/pro-deal my way into a new frame every year for a couple hundred bucks and never worry about breaking one. I went for aluminum for that reason.
I also have a hard time believing it's one lb lighter. I think 4.5/4.7 lbs for a medium (versus 5.2 for mine) is reasonable.