Topics that seem to be of interest and most of them were already discussed at developers meeting in Ottawa are 1.) parallel sorts 2.) parallel query execution 3.) asynchronous I/O 4.) parallel COPY 5.) parallel pg_dump 6.) using threads for parallel processing
[...]
2.) Different subtrees (or nodes) of the plan could be executed in parallel on different CPUs and the results of this subtrees could be requested either synchronously or asynchronously.
I don't see why multiple CPUs can't work on the same node of a plan. For instance, consider a node involving a scan with an expensive condition, like UTF-8 string length. If you have four CPUs you can bring to bear, each CPU could take every fourth page, computing the expensive condition for each tuple in that page. The results of the scan can be retired asynchronously to the next node above.