We map some of our multiple selection attributes to pick list that contain large data sets (WS based and 50k+ records). in our regular business, we also tend to more than 50 items regularly to a multiple selection attribute. such combination of large data sets and having to repeatedly search and select items over and over is not a great use of anyone's time.
Should FLC provide the ability for users to copy and paste data either in delimited form or from a spreadsheet, it will greatly improve the user experience as well as the reduce the human effort.