>> However, what is the max number of database I can create before
>> performance goes down?
>
I know I'm not directly answering your question, but you might want to
consider why you're splitting things up into different logical
databases. If security is a big concern, you can create different
database users that own the different departments' tables, and each of
your apps can login as the corresponding users.
Everyone loves reports. Once you've got data in your database, people
will ask for a billion reports...Whether or not they know it now, most
likely they're going to want reports that cross the department
boundaries (gross revenue, employee listings etc.) and that will be very
difficult if you have multiple databases.