I'm currently working on a Sun BluePrints article, for the moment titled "Migrating Sun Java System Messenger Express Personal Address Book: Using the pab2abs.pl Utility." Some background: when you upgrade from Messenger Express, with its own personal address book (PAB) to Communications Express, you get a new address book (Address Book Store, or ABS). And of course, we make you migrate the PAB entries (that is, the migration doesn't happen automatically.) Turns out that the runMigrate.sh script provided since Communications Express 6 2004Q2 has, shall we say, some issues with large PAB databases. So one of our engineers has come up with a new tool that uses Java System Directory Server bulk export and import (as opposed to modification or creation of entries over LDAP), which much improves (speeds up) the process.
Look for this Blueprints article and new tool to appear very soon.