I found errors in a downloaded report, and to save myself time, did all the updates in the Excel file instead of searching out all 1000+ records individually, and then re-running the report.  When I tried to use the Import tool to overwrite the corrected information, and got to the duplicate check, almost 90% of the duplicate records it gave me were the spouse of the person whose record I was trying to correct--as though it wasn't even cross-referencing the account names to understand that John Doe at 123 Somestreet and Jane Jones at 123 Somestreet were different people. 

Which means that I have to work through the ultra-annoying account search to find each individual record, navigate to the correct page on that record, and then update the information--which will take hours, instead of the 20 minutes that a proper upload should take.