I started with bikes in the 22-23 pound range and after changes over the years my bikes are now 15-17 pounds. What I've figured out is I don't have the motivation to ride faster going up hills but going slower is now much easier!!! And I like that!

My experience has been that it is easier to stay in groups and ride wheels on rolling terrain with a lighter bike.....close gaps etc. While overall weight (body weight plus bike weight) makes a lot of difference, for riding in groups lower body weight (somewhat correlates to fitness) plus a lighter weight wheelset are the things that have helped me the most.