Is maintaining a single database an issue when the underlying project becomes larger?
I think you are correct in your answers and JNK is correct about locks. I see some reasons to have multiple databases.


Replication. If parts of your database should be replicated to local read servers they benefit from being on different database. I don't know about sql-server specifically but in mysql (and generally) a master can only maintain one binary log per database and if table A and B should replicate to some server and table C and D should replicate to another server than those needs to either be on different databases or the binary log needs to be filtered on the slaves.
Uptime and accessibility. If different parts of your data have different requirements on uptime and accessibility it would make sense to put them on different databases. One could have hot standby with all data replicated and the other could have a nightly dump.


But again, I think you're right :)