If anyone has any input on Yosemite's performance on some of the oldest supported systems, e.g. 2007 iMacs and 2008-09 Macbook/Macbook Pros, please share. Based on my experience, it does tax performance quite a bit.
MacBook white unibody late 2009 here. It's working great for me My macbook is a lot faster and smoother than with Mavericks, and there are no new problems. So I'm happy