2. You can return a cursor from a function today, but I'm not sure about yesterday (in plain English, yes in the upcoming 7.2 Beta but I'm not sure about 7.1). As Ben mentions, work is underway to allow PL/pgSQL to return rowsets. SQL functions can already return rowsets but of course this isn't as useful.
3. You're right about aggregates being very cool. I've not played with them other than test cases because there's no equivalent in Oracle or any other RDBMS I'm aware of, so they're not portable and therefore I've avoided looking for uses in OpenACS. But they're still awfully cool!
4. There's no direct way to do this in PG, same as in standard SQL. It's only working in Oracle due to sheer luck, after all...
