As a follow-up to my system jobs post earlier this week I was pleased to find and to have shared with me two other related posts.

Customer Effectives post titled "Bulk Deleting Waiting Workflow Instances from Microsoft Dynamics CRM"

and

Phil Adam's Blog post titled Performance is slow if the AsyncOperationBase table becomes too large in Microsoft Dynamics CRM 4.0

Both add additional insight on the subject matter that is well worth the read.