Joe,
Integrations 4&5 are the most valuable for Ally. Knowing the tax before the order is created would be useful for budgeting purposes but the practical issues of invoicing against a PO tax line item offset the advantages IMHO. With the states desire for increased revenue, I can only expect this area to get more complex and subject to error. I also expect for the states to do more audits on companies for sales and especially use tax shortfalls.
I would like to see two solutions from Ariba. The first is a standard integration 'API' with the major tax vendors like a punch-out catalog or web service. The second would be a more turn-key service offering like ICS.
Russ