I don't think the version upgrade would really affect this. This is a great, out-of-the-box solution, with Outlook.
You should be able to give Domain Users group access to the site or the form library and not have to worry about individual permissions or creating a SharePoint account. You may mean the setting up of alerts for bosses.
One questino I had is with Lotus notes, if the user does a Send To Mail Recipient from the File menu, does this work? If it did you would just need to instruct users how to manually email the form, but this may require Outlook too, I cannot test.
Otherwise you could promote the approvers email into SharePoint as an additional field. So completed forms would be listed with the email address and someone could manually monitor the form library and email links out for approval. Not ideal but could be better than a paper process.
Losing the email submit makes it pretty difficult, I would be frustrated too. You may want to look at the Database Accelerator Download. If you want to pursue Electonic Form Solutions with InfoPath then with this and our catalog format you can create your own workflows, assignments, and approvals within InfoPath using a SQL database. It gives you active directory access, secures your forms, integrates with SharePoint, gives you lots of other great functionality. I would check it out and see if it might help you.
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