1) When I used to interact with a notification, it wouldn't behave as it should.
For example, with iTunes songs notifications, if I clicked "Skip," it would skip but it would also bring up iTunes. With Messages, if I quick replied, it'd bring up the Messages screen. Kind of defeated the purpose of quick replies and such. Then, if I had a web notification like MacRumors and I clicked it, it wouldn't bring that up.
So basically it would open windows when it shouldn't have and wouldn't open windows it should have. Now, it seems that has been fixed.
2) Handoff is working much better for me, now (iPhone 5s, iPad Air, Late 2013 27" iMac).
3) AirDrop is working much more reliably for me. Almost always works now, vs. before when the iMac and iOS devices could rarely see one another.
4) Everything in general seems much more responsive. I wasn't having very much problem with unresponsiveness previously, but it did get "stuck" now and then. Haven't had any problems with that since updating.
EDIT:
5) Facebook scrolling while typing issue is no longer present.