Noosfero should be able to receive a list of users from e.g. a CSV file and automatically create accounts for all of them, sending a automatically-generated password by e-mail. The CSV file should have at least a login name and an e-mail. Ideally the CSV file could have any number of columns, and the admin would map the CSV columns to user attributes during the import process.
egroupware has a similar feature, for importing contacts. Take a look at it.
-- AntonioTerceiro - 04 Jan 2011