Functions returning sets

Sorry to gripe here. Don't get me wrong, I think Postgres is amazing, and I
think all you guys do an amazing job.

Is it just me, or do others agree, functions returning sets need to be able to
be used in a select where equal clause.

select * from table where field = funct_set('bla bla');

Where funct_set returns multiple results. This currently does not work. The
only other option with sets is usage like:

select * from table where field in (select funct_set('bla bla')) ;

Which would be OK if it were able to use an index and preserve the order
returned.

Without the ability to use a set to select multiple objects in a join, it is
dramatically limited in use for a relational database. In fact, I can't think
of many uses for it as is.

Having used Postgres since 1996/1997 I have only a very few gripes, and I think
7.1 is a fantastic effort, but, I think a HUGE amount of applications can not
be done because of this limitation.

What can I do to help get this ability in 7.2? I is VERY important to a project
on which I am working.