Not a surprise. The more you shrink down the machine, the more cooling becomes an issue.
Some people have had overheating issues due to their fans. Most haven't. I've read plenty of people playing their machines for hours on end without an issue. Here's a noise and heat test Digital Foundry did on both the X1 and PS4: X1: PS4:
The PS4 draws more power, is basically the same noise level from 3 meters away, runs warmer at idle and while playing a blu-ray, but remains cooler while running a game or running a game + bringing up the UI.
This post was edited on 11/20 at 10:01 am