How many Cluster database on a single server

Hi everybody,
I googled a bit around and also checked the mailing lists but I still
can't make an idea. We plan to use postgres 9 and the Cluster Database
Replica.
My colleagues are asking how many Cluster Databases (initdb) can I
create and run on a single server. I mean, supposed my server has the
resources, can I create 100 or even 200 Cluster Databases? Everyone with
the right configuration and in respect of the requisites?
Or the postgres architecture doesn't provide similar numbers?
We are thinking to use the replica from near 200 databases around the
internet on a single db server.
Does anyone already did something like this?

BTW, this is my first email to postgresql mailing list. If I'm doing
something wrong do not hesitate to correct me :)

Thanks
Davo