One major culprit is the practice of keeping large email attachments. Another consumer of disk space is the Eudora trash folder.
Some students use it for a filing cabinet.
This not a good practice since it confuses the messages that are keepers with ones that need to be deleted. Always keep the two separate, and empty your trash each time you logout. To that end, the Eudora program used in the labs will automatically empty the trash folder whenever you quit the program.