Wheel weight I notice. I went from a 15.5 lbs bike to a 17 lbs bike that has lighter wheels. The 17 lbs bike is great. I won't say it's heavier or lighter feeling; the wheels were all of 150-200 grams lighter. But going from wheels literally 2 lbs heavier... huge difference.

There seems to be cusps of "perceived weight". Just roughly I'd set the divisions at 28 lbs, 25 lbs, 21 lbs, 19 lbs, 16 lbs, and about 13-14 lbs. The first few weights pertain mainly to mountain bikes. I guess in the same ranges all the time "Oh it's about 16 lbs" when it's 15 or 17 lbs. The really light ones are 12-13 lbs, those astonish me.

As far as weight goes... except when going to tubular tires, light bikes can be used every day. If you trade time for money, you can build a very light bike for a minimal amount of money. It may take a couple years, but it's possible. A young racer, maybe 22-23 years old, had a 12 lbs bike that he'd built up for about $2000 (2007?). With clinchers it'd be 13+ lbs, but still very light.