I was onsite with a client of ours last week and ran into some interesting scenarios when troubleshooting a Forms and Client issue.
The Forms issue was when we were trying to save a form to the repository and populate the template data. There were a number of fields assigned to the template, but the two causing issues were named 'Approved By' and 'Submitted By'. When we tried to have Forms populate those 2 fields it would not. It would save the form into the repository with all the other field values populated. Once in the repository, we could populate the fields without any problems. We changed the names of the 2 fields and were able to successfully save values to them from Forms. Once we changed them back, it didn't work again.
The other issue comes when trying to add a field as a column in the Windows Client. The field name was 'Document Name'. The field did not show as an option to select from when viewing the different fields.
So the questions is, are there reserved names that cannot be used when creating fields?