Foreign Database Connectivity

I have been thinking about this for a while. Now that we have a 
practical methodology for returning full rows from functions, we could 
make this sort of thing pretty "easily."

How should it look? How much work is worth putting into it?

My thinking is that there is a module in contrib or something that 
enables this.
The foreign DB link module should be able to load external DB drivers, 
this way anyone can add a new DB to the system.
We should start with DBF files, ODBC, and of course, PostgreSQL.

Does it need to look like a table or can we get away with it being a 
function?

If we make it a function that's easier.

Any thoughts?