I have measured the idle temp of my macbook air 11 inch 1.4 Ghz, 4 GB, 128 SSD (2014 model) at a room temp of ~22oC and I get idle CPU temperature around 40oC (one safari tab open on apple.com and iMessage app active...)
The macbook retinas (MBR) appear to be a bit warm to the touch (both underside and top near the central part of the speaker grill (where the mainboard is located) compared to my macbook air and pro, which when idle are cool...
Im interested in what the idle CPU temp is... I plan to buy a macbook retina to replace my air and intend only light usage (reading PDFs, web browsing, word and excel document editing etc)... the screen on the machine is a joy to use
I do like my air as it is speedy, runs real cool and has fantastic battery life for what I do, only downside is the terrible display... this is whats making me think about replacing it with the MBR...