I have a mid-2013 13" MacBook Air and I like to use the keyboard whenever possible as opposed to clicking.
In Mavericks I could open Launchpad (Fn-F4 in my case), navigate to a folder using the arrow keys, open that folder with the return key, navigate to an app icon using the arrow keys, and open that app with the return key. All good.
In Yosemite (OSX v. 10.10) I can open an app that way only if it's in the top level of Launchpad. If I'm inside a folder in Launchpad, I can navigate around using the keyboard but cannot open an app using the return key. Nor can I open an app with command-O or any other key that I can find. (Inside a folder, when I navigate around, the background of the selected app icon turns a light gray instead of a darker gray in the top level of Launchpad. I'm not sure if that is significant in some way.)
This is puzzling to me. Any thoughts? Thanks in advance.
[Update, Sept 18, 2016: Launchpad launches apps as expected with the return key in this situation as of OS X El Capitan, version 10.11.5. No more bug.]
Best Answer
LaunchPad was designed as a primarily non-keyboard UI for opening apps.
A drastically easier way to launch an app via the keyboard is to use Spotlight under Yosemite. A simple Command-Space, then the first few letters of the app name, then press return.