Well, in theory, with a fully decrypted HDD, it may be possible to take a closer look at the inner workings of the PS3.
Furthermore, it would be quite easy to distribute downloaded games (PSN) to others, assuming that the DRM was also (somehow) copied over.
The DRM may be stored in the system database, which (like everything else) is on file somewhere.
The question is, is that file still encrypted?
However, we will not be able to do any unsigned code from the HDD with this - as the system will not allow unsigned code to run from the HDD.