Bugzilla's bug moving features are fairly inadequate. As wirdal writes, we need to handle a few different things between Bugzillas: Moving of bugs, intra-installation dependencies and duplicates, and perhaps a "see also" field that works like dependencies but also between installations.
The main issue is how to track users between bugzilla instances. Two possiblites were discussed on #mozwebtools today: 1) When BZ1 moves a bug to BZ2, the bug on BZ2 is attached to accountID used on BZ1 if it exists on BZ2 or new account with same accountID is created. 2) We're switching accountID from user@host to user@host#bugzillaID, and when BZ2 does something and wants to send email to this user, it simply checks bugzillaID, send info to BZ1 and BZ1 track it.
*** This bug has been marked as a duplicate of 123130 ***