All Borg (Seven of Nine included) undergo "Regeneration", which can be considered roughly the equivalent of "Sleep", which perfectionists such as the Borg would view as inefficient in their search for ultimate perfection.
184.108.40.206 08:07, March 17, 2010 (UTC)
Several times in Star Trek: Voyager, Seven is seen to "regenerate", standing up, in one of her Borg alcoves, located in one of Voyager's cargo bays. Whether or not she needs to sleep too, is not explained. ProfessorTrek 21:20, July 16, 2011 (UTC)