OK OK, not a great pun - but multi threading has finally come to hte BIP engine in 10.1.3.3. You are not going to see much if any improvement on single CPU or single core CPU machines but if you are running on something a little more meaty - crank it up baby!
The doc is short and sweet on this - http://download.oracle.com/docs/cd/E10383_01/doc/bip.1013/e10416/bipperform.htm#BABBBFEG
Im pointing it out because, as I have mentioned in the past, our main User/Developer documentation has not been updated - we are having to put information into the new features guides for each release - they will sync up I promise.
Before you EBS, PS and JDE folks ask - nope, you do not have this yet - I know I know, you are all running multi processor machines and this would help immensely - its coming.