David - I know we have a feature request open on allowing more customization of the buckets that the "Group By" filter sorts things into. If you email the
support ninjas, they can add your email to that item in our development database.
For the 1.0 release of OmniFocus, we tried to pick default values for those buckets that would be a good foundation; if you try to do everything perfectly, you never actually ship the product. :-)