Here are the significant limitations that we anticipate affect a large number of users:
Code Imports does not support submodules, because Bazaar does not yet support them (Bug #402814).
If bzr cannot merge the packaging branch into the base branch (e.g. due to parallel imports), the "nest" command must be used. If the "nest" command is used, the packaging branch must be the contents of the debian directory (rather than containing a debian directory). (Bug #627119)
Builds of private branches are not currently supported. (Bug #607895)
Import fails with infinite recursion through _reconstruct_manifest_and_flags_by_revid (Bug #519709)
Launchpad disallows valid CVS module of '.' from being imported (Bug #594294)