Just echoing your platform difference comment.
I've noticed that the editor, with my load of plugins, comes up relatively quick on OSX (~4 seconds from launching, equally as long to open a new window), and roughly twice as slow on Windows (~8 seconds from click, ~3 seconds to open a window)
But, when I'm using it, I'm basically living in the app, so the startup time is really a moot point IMO.
I do still resort to vim on the command-line for some things, but as a "daily driver" code editor, Atom has been excellent.