The default settings for a ext{2,3} file system is to reserve 5% of the file system so that only root can access it.
This was great back in the day when user accounts filled a drive to the max and everything was on one partition - not so when we're lean and mean and want some extra space.
To change your reserved block count to something a little more nice simply do this.
Code:
#tune2fs -m 1 /dev/udba
Where /dev/udba is the partition you want to change. On a 1gig partition, you're looking at about 60Meg free increase. Of course it's expotential to larger drives, so a 80 gig partition might regain 5gig of space.
To check out what your file system is doing, simply use tune2fs again.
Code:
#tune2fs -l /dev/udba