Here's an interesting read courtesy of kotaku. Nikkei electronics took apart a couple of xbox 360's and measured the temperature as well as looked at the design of the heatsink and placement. They also looked at a repaired xbox to look for changes.
http://techon.nikkeibp.co.jp/english/NEWS_EN/20070801/137224/
Highlights:
"When designing consumer products, it is common to seek a temperature gap of around 10°C between exhaust and room temperatures," the thermal design expert said. "The 22°C is quite a large gap, in the first place."
The cooler fan's maximum wind speed was 1.1 m/s, only 1/2 to 1/3 compared with general desktop PCs. It may be partly because the fan rotation was reduced to lower noise. According to an expert's analysis, "The amount of switched air is slightly in short considering the chassis' size (309 x 258 x 83 mm3)."
"The heat sink on the graphics LSI is so small, I wonder if it can really cool down the board," our expert said.
In the Xbox 360, however, the duct was cut off before the heat sink and the DVD drive, and, instead, chassis took up the heat sink's upper area probably due to limited space inside the chassis.
