Hosting options on Postgres - what's best?

Hi,

I'm looking into creating a hosted application with Postgres as the
SQL server. I would like to get some ideas and oppinions about the
different ways to separate the different clients, using postgres.

The options I had in mind:

1) Create a different database per client. How much overhead will this add?

2) Use schemas and authentication. So each client is a different
schema on the database.

3) Use application level security (per object security maintained by the app).

4) ????

Any ideas? Opinnions?

js.