There have been many requests on brainstorm for different disk management utilities, and all of them can be summed up into one configuration GUI. This would (in theory) have the following setup:

Tab 1: Free Space
-integrate Baobab (and remove it from the applications menu)
-create an extensible disk cleaner with default plugins for emptying the trash, clearing the firefox cache, possibly deleting logfiles (using policykit), etc.

Tab 2: Health
-allow setting frequency of fsck, so an option something like:
[x]Automatically check my disks every [35] boots.
-a button for immediately checking all filesystems
-S.M.A.R.T. integration

Tab 3: Backup
-a scheduled backup utility that can image the entire disk or zip certain folders using cron.
-allow creating multiple backup 'profiles' for advanced scheduling
-incremental backup would be nice, but probably difficult

Tab 4: Advanced
-integrate the partition editor from the installer, and enhance it to allow fstab editing as well

The exact implementation of the above features/tabs is up for debate, but the concept is far more important.

This would address a huge number of brainstorm ideas floating around, and I think is a great candidate for the 'main feature' for 8.10 (like compiz-fusion was for 7.10).