It is better to "import" the complete library (including the playlists).
In MC11:
File > Library > Backup Library...
In MC12:
File > Libary > Restore Library... (restore the backup file you created with MC11)
If you don't want to do the backup/restore proces you can export the playlists in m3u format in MC11 and import them to MC12 with the Auto-Import tool (you can select the "m3u" file type in the tool options). The imported playlists should appear in the "Imported Playlists" group.
