I have a few things that I feel should be noted:
- ~/Library has been hidden by default for a number of OS X releases. That's not new to Yosemite.
- It's possible to un-hide things from Terminal.app without installing any 3rd-party software, but most users probably won't want to do that.
- Hidden folders can be accessed from Finder if you know their name. For example, to get to the ~/Library folder even when it's hidden, select Go->Go to Folder... (Command + Shift + G). Then enter ~/Library into the box.