Playlists are stored in the playlists table in the sqlite3 database ‘songs3.db’. The column ‘type’ determine the type of playlist. I believe the values are:
0: Internal static
1: Smart
2: External static
I guess you could write a sql script that would extract the smart playlist criteria and save it in a file in case you needed to recreate (if the database became corrupt)
select * from playlists where type = 1