In my experience using dotlrn at Sloan, I have found that CSV bulk upload files with greater than 50 names fails or the browser times out (which means you have to add users to a group manually one at a time), so I break larger files up into smaller files.
You also have to make sure that your CSV file is "clean" - without any extra spaces at the beginning or end of the file, so I check each file using notepad beforehand.
