After some digging with Google, I found Greenspan:
http://www.alexium.com/greenspan. He used the gnucash datamodel on oracle to implement a light quicken type application in ACS 3.x. It's been in "pre-alpha state" for the at least the past 8 months (by my recollection).
I agree wholehartedly that the OpenACS4 will be ripe for Enterprise applications. GNUe would definitely be the way to go, if there is a workable integration scenario. If I remember correctly, GNUe uses CORBA to interface with it's datamodel and is designed for seperation of presentation & busines logic, so it seems likely.
