So far everything still fits on my MacBook Pro (500GB hard drive). I delete a lot of shots I take and haven't been out to shoot much recently.
I have a synology NAS with 3TB (2x 3 TB Raid 1) for backup only with TimeMachine and occasional rsync backups just in case TimeMachine blows up.
Once my library grows, I might add additional storage, either a second NAS or external drive and move the master files in Aperture.