UPDATE: The following information is for the diags partition that comes factory installed on the new kindles shipped with 5.1.0. The 5.1.0 update package does not install these changes on a kindle with older firmware. I flashed this new diags partition to my kindle touch, and there is an image file available with SSH pre-installed (see the "simple debricking" thread for download links).
I just compared that 5.1.0 diags image to my virgin 5.0.0 diags image. There are 153 files that are different, but a lot of those are symlinks.
5.0.0 diags: /etc/version.txt:
Software System Version: 137022-diags_signed-137022
Thu Nov 3 11:23:42 PDT 2011
5.1.0 diags: /etc/version.txt:
Software System Version: 137333-diags_signed-137333
Wed Nov 9 15:20:31 PST 2011
The shadow files are different too (as expected). The root passwords have different hashes. The diags root password is fiona180, which is probably derived from the serial number of the kindle that contained this image. For the diags_ssh, I changed the root password to use the mario hash, so it was not locked to a serial number.
/etc/guid is different too (also as expected).
/etc/fstab is different. It now contains the nfs mount , and the usb drive now had "nonempty" removed from it.
Many binary files are different in /bin, /sbin, /usr/bin, and /usr/sbin.
libcrypto.so is different.
mx50_yoshi_mma8453.ko is different.
And... /opt/factory/system_diags is different!
This means that my jailbreak "secret" method might not work. I will need to flash this and test it.
So... in general... EVERYTHING that matters is DIFFERENT in the new diags partition that comes installed on new kindles.
EDIT: Thanks thomass!
UPDATE: /opt/factory/diagrootfs_md5_list is different. Specifically. these lines have changed:
Also, there is a new file: /opt/ar6k/target/AR^003/hw2.1.1/bin/AR6003_calfile.bin
----- old -----
----- new -----
(As mentioned above, these changes are not installed when you update old firmware to 5.1.0 using the firmware update install package.)