"As for the heat and fan volume, per a suggestion from Marco Arment (Instapaper creator and friend of The Verge), we ran CPUTest for 12 minutes to see just how loud and hot we could get the machine. There’s good news and bad news: while the fan was surprisingly quiet — even in an apartment with closed windows and some light traffic and rain outside, I could barely hear it — the heat was in the ballpark of what we’d expect from our personal 2011 MacBook Pro. Which is to say, hot — particularly the metal rim around the ‘U’ key, which is about where the processor rests internally. It's hard to touch for more than a few seconds."
via
http://www.theverge.com/2012/6/13/3082649/macbook-pro-review-retina-display-15-inch