Indeed - I am currently pulling out queries that are using parallelism and looking to tune them as a start. Then hopefully I will get a good idea of what the threshold cost should be.

There is a lot of churn in the the plan cache though it seems so finding all the plans may prove difficult.

I have also read about finding the thread that doesn't have a CXPACKET wait to see what the actual cause of the waits are, and am having a think about how to actually capture this, it will no doubt invlove writng something to query sys.dm_exec_requests.