Well, there have been a few initial reports - or complaints rather - that the phone gets heated up while using apps like SnapChat or YouTube. Please note that the apps mentioned are quite heavy on resources . If one or two such apps are open and working in the background, it is quite natural for the phone to get heated up.
There have also been few reports that indicate that the phone gets heated up near the camera module. If the temperature goes up by a few degrees, it may not be a concern. If it, however, becomes a regular phenomenon, you may need to consult service or get your device replaced.
Live....and Let Live!