The one thing that intrigued me about Atom is that it would actually run in the browser, meaning somebody would create a version you could load up in chrome/safari/firefox and connect to your github account etc. However I haven't seen anything of the sort yet. Does this exist?

Locally, I've tried Atom every now and again and even with the new improvements in 1.1, as soon as you get above a certain threshold in number of lines it starts to slow down considerably (>= 250ms key-press, subjectively) which would only be acceptable if I was running in the browser and even then would be barely useable. Come to mind, the cloud9 ide feels 'snappier' that Atom.