The elements of blogging that I would focus on, for marketing purposes, are:-
- a journal or 'yearbook' of their time at university (as mentioned in someone elses answer)
- a forum or means of contact for clubs/societies
*access to reviews, news etc on the latest books, dvds, cds, as well as a chance for them to give their own views
- i also thought the idea of it being a means of contact with friends and family back home would be quite appealing to some first year students
As for how to promote the system – links and or ad's on both the University insite and the Student's Union sites could be useful in addition to flyers in the pack of info from IT services that they get when they move into their rooms.