I really don't see anyone would need to use more the 5, ever. Your never going to be using 5 at the same time, so why don't use use one database for multiple things? I know a lot of scripts allow you to use something before the actual data, so it can be reused. I think innovation is the price of a new database.
If you prefix your tables in you're databases you can fit alot of data into one DB, for ipb forums the prefix is ipb_ and phpbb has its own prefix which means you can install alot onto one db. I havent tried this but it must be posible, 5 Databases is more than enough.
Me neither, i would rather have 1 database to 1 script. It is easier and is easier to maintain and backup if something goes wrong. Since some database script can sometimes have error, merging 2 scripts into 1 database without a good knowledge of what you are doing will most likely end up in more errors etc. Even though i know it is posible, Is there anyone here who would actually have the time to figure out how to do it and actually do it?