Initial impressions are that this would not work in my problem domain as I had originally tried DBI::ODBC for accessing the SQL Server and was getting truncation errors on selecting the data (ie before even hitting MySQL).
The solution I have provided uses ADO natively and so avoids this problem. Additionally, I can just about guarantee that the migrate module will not handle Memo fields correctly either (though of course I could be wrong ;) ).
Your migrate tool looks good but I don't think it is ready for the whole porting from ADO land to MySQL land that I needed.
Thanks all the same.