In the fwiw category, based upon my observations from our just-completed migration (under conditions very much like those described here) of ~90 BB7290s:
A security wipe of each device will be necessary, unless the kill command spawns that process, so as to sever the device from the previous BES IT Policy.
There is some
data which resides locally on the device - saved messages; image files that have been saved to the handheld (and possibly used as standby or home screen background); profile configuration changes; Autosig text; phone history/logs; BrickBreaker score
; Password Keeper info (I expect it is local only - our users don't use it).
Since our IT Policy precludes use of Browsers and SMS, there are likely other data which would belong in the list above (history, bookmarks?).
We chose to perform a tethered backup of each handheld on an admin workstation (meant the users all had to turn the devices in with the password), and have the data available for later restore/selective restore if asked. Doing a full restore after the security wipe seemed to introduce problems with the subsequent Enterprise Activation on some handhelds (all were done OTA - over the air).
Our users email was migrated from EXCH 5.5 to EXCH 2003 in a new domain and organization. Then the BlackBerry users were removed from the old BES and added to the new BES (each BES has its own DB). Then the BBHHs were brought in for backup/wipe/re-activation (EA).
As blackberry1 said - there is no reason to try and preserve info from the old BES database afaik.
Hope this helps!