It seems like
Microsoft has listened to all the complaints about the hot running Xbox 360 and has finally decided to install a new heatpipe and heatsink next to the GPU.
This will hopefully fix the overheating problems that some Xbox 360 users have encountered.
However, it is not clear if this is a fix for repaired machines or if it actually ships pre-installed in newer consoles.
The Xbox-Scene has some more picture as well as a video of the new heatsink and you can find it here