I weigh 154 lbs but dropping my bike down from 30 lbs to 20 would be a definite improvement and would see noticeable gains, especially on the climbs. Weight may not be the be all and end all but it sure is an important factor.

Weight is important, and even a small difference can be noticed. I think a lot of folks play this down due to the cost associated with low weight bikes. However, a low weight bike will never fix the problems of lacking skills or poor conditioning. Getting all of these "right" and together is awesome!

It's mainly why I bought my current bike, if I can drag a heavy hardtail around fairly quickly, my fitness and skills should be on point in about a years time when I upgrade.

Weight is important when we are talking about 10lbs not so much when we are talking about a .1lb and it also depends on where that weight savings comes from. Wheel weight makes a lot more difference than say dropping seatpost,stem, or handlebar weight. If you have the cash it takes to both drop weight and maintain the component's strength go for it. I got a good deal on some stan's crest wheels 1550grams which dropped about 1lbs over the crappy wheels I was running. Downside to that is they have a 180lb weight limit and are rather flexy in turns and rock gardens so I had to be more careful and no jumping on my full squish. Swapped those to the rigid and put 1700gram all mountain wheels on the squishy bike and back to jumping and plowing through turns and rock gardens. I can't justify spending the money for a set of 1500gram carbon wheels that are also very strong.

The carbon rims that came with my Epic are solid as can be, have been ridden over a lot of large rocks, and get airborne frequently. However, when building my SS MTB, I had to choose between alloy and CF. the weight difference was small, between the recommended rims, but the price difference was enormous. I went with the alloy rims, and I am very happy with them. Plus, in the end, the bike still came in at just over 20 lbs.

Cost/benefit is where things get complicated. I would have loved to get HED Big Deals for my fatbike. 445 gram 85 mm wide rims? That is 220 grams (about half a pound) lighter than the DT Swiss BR710 rims I got. But the HED rims are about $1000 a piece and the DT s are about $150.

Would saving about a pound of rotational weight help me? Hell yeah. Is it worth an extra $1,700? Not for me right now. But if I could afford them, I may get them (or Kuroshiros which are a tad heavier but stiffer)