Definitely have noticed a significant improvement in the smoothness and reactivity of safari, which to be honest is the program I'm in the most on my rMB. Feels like the GUI is generally a bit zippier overall throughout the computer as a whole. As for battery life, I think I've noticed it being running down slightly more quickly than before all though this is pretty unscientific. It just feels that when I glance at the b developed from using it for a couple of months so far with yosemite. Pretty sure this isn't an illusion, but it's not a dramatic drop and like others have said, I'm sure that if power use has gone up, they will be looking into doing what can be done about that in subsequent point updates. Could be that it's an unavoidable thing - if this new metal framework or whatever it is that allows for the graphics to run a bit faster and smoother necessarily uses a little more juice, then that could be that. In any case, I think it was worthwhile because it's obviously nicer to have a machine feeling fresher and snappier than it did before with a new OS upgrade rather than the other way around.