I've got a couple tables that are populated by a back-end process that will be used only by the front-end WP site. They are pretty flat and no-nonsense. Currently I have these tables in their own mysql database, but I'm starting to see that WP has some built in mechanisms for querying its own database that might be a little more efficient/wordpressy.
leave tables in separate db, create an additional database connection using standard php/mysql functions and query away.
put tables in WB db, use the wpdb->xxx() functions to access them.
would love some opinions!