To perform the migration, you can use the AppleShare IP Migration utility that Apple provides with OS X Server.
When I started the migration process, things began to get, well, interesting is a nice way of putting it.
First, the user and group information. Before you migrate, you set up a user with a new and distinct name (I used "Daffy Duck" or "Bugs Bunny"), and then use this new user to set up a default (I called my default "Staff"). The default is then used in the migration process, applied to all the migrated users.
There's one flaw in this user and group migration process. While AppleShare IP accepts quite long names for groups, OS X Server will only work with a short name of eight characters or less, and the import process sets both the group name and group short name to the same group name from AppleShare IP. (OS X allows names longer than eight characters, but then breaks when you use themgo figure. It also fails to warn you if any of the short names are now longer than eight characters, so remember to fix this problem once you have the groups in OS X Server.)