This has already been discussed before, the processor is right on the Emblem.
If you go back and look threw the tear down you can see that's where the processor rests.
I had a 16gb PB which had a "bump" at the BlackBerry logo and I really felt the heat when I worked the device really hard (i.e. NFS, videos, etc. all going). I moved up to a 32gb which doesn't have the bump at the logo, and the heat is much less noticeable.