I would like to edit due dates in table Bill in a spreadsheet-like format. 

From other posts and trial/error it appears that getting a read/write link from Excel/2007 is not possible, even if you set the mode to ReadWrite or "Share Deny None" in the connection strings.

I can get a read/write link from Access, and edit the datasheet,  but it is very slow. 

I think my only practical alternative is to allow the user to update in Excel, then write an VB/ADO routine to update each change.

Correct?

Correct. Just about everyone I've seen ended up moving their application out of MS Access. MS Access is intended for its own MDB or MS SQL Server backends only.

The fastest way to use QODBC in MS Access is to execute SQL statements directly like this:-

DoCmd.RunSQL "INSERT INTO QB_InvoiceLine ( RefNumber, InvoiceLineItemRefListID, InvoiceLineDesc, " & _
    "InvoiceLineQuantity, InvoiceLineRate, InvoiceLineClassRefListID, InvoiceLineTaxCodeRefListID, " & _
    "CustomFieldVFBatchNo, FQSaveToCache )" & _
    "VALUES ('Me.RefNumber', 'Me.InvoiceLineItemRefListID', 'Me.InvoiceLineDesc', 'Me.InvoiceLineQuantity', " & _
    "'Me.InvoiceLineRate', 'Me.InvoiceLineClassRefListID', 'Me.InvoiceLineTaxCodeRefListID', 'Me.CustomFieldVFBatchNo', 0)"