As soon as its announce that OS X Yosemite is launched, I immediately do the upgrade last night. It took almost 15 hours to download. This morning I completed the installation. Everything looks fine. Then I also do some applications upgrade. I saw 7 apps need to upgrade in App Store.
My first impression on the UI is mixed, exited because its brand new OS X, but feel uncomfortable with the new font, buttons, new colour used, imperfection on icons and some new small changes on layout. The feel is different. I've been using Mac OS since its first version, this is the first time I have different feeling.
I store Music Library, Time Machine, and File Sharing on network drive. I
Additional important thing is to update Java for OS X 2014-001. If you haven't done it, you can download it here.