v5.3.0f4 on Ubuntu 15. Generally working (yay!) High CPU usage (already known issue)... but only when you are *not* in Play mode! Guessing default Editor framerate is set too high, which is forced to something more reasonable when game plays and brings it back down. In case this datapoint is useful to anyone...
I'm also seeing this as well on Arch Linux, Unity version 5.3.1f1. Is there an open bug for this? Or how might we track the status of this?
Just installed the editor and hopped on here to see if this was already reported. I did not notice that CPU went to normal while in play mode, but thanks for that tip! Now at least I can put it in play mode while reading tutorials and not have my laptop fan sound like a jet engine.