@Colin re comment #14: I'm not sure that I understand "filesystem corruption in the context of hibernation".  The system hasn't been hibernated since installing Natty on the /dev/sda7 partition.  Today's Natty upgrade did the following:

Setting up grub-common (1.99~rc1-8ubuntu1) ...
Installing new version of config file /etc/grub.d/10_linux ...
Setting up grub-pc (1.99~rc1-8ubuntu1) ...
Installation finished. No error reported.
Generating grub.cfg ...
Found linux image: /boot/vmlinuz-2.6.38-7-generic
Found initrd image: /boot/initrd.img-2.6.38-7-generic
Found linux image: /boot/vmlinuz-2.6.38-6-generic
Found initrd image: /boot/initrd.img-2.6.38-6-generic
Found memtest86+ image: /boot/memtest86+.bin
Found Windows 7 (loader) on /dev/sda1
Found Windows Recovery Environment (loader) on /dev/sda2
Found Windows Recovery Environment (loader) on /dev/sda3
done

Maverick is installed on /dev/sda5 (and it's grub is the default install):

 sudo fdisk -l

Disk /dev/sda: 320.1 GB, 320072933376 bytes
5 heads, 63 sectors/track, 1984579 cylinders
Units = cylinders of 315 * 512 = 161280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x135c058f

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           7        1301      203776    7  HPFS/NTFS
/dev/sda2            1301      651462   102400360+   7  HPFS/NTFS
/dev/sda3         1905278     1984571    12488704    7  HPFS/NTFS
/dev/sda4          651463     1905277   197475862+   5  Extended
/dev/sda5          651463     1738212   171163093+  83  Linux
/dev/sda6         1868262     1905277     5829988+  82  Linux swap / Solaris
/dev/sda7         1738213     1868258    20482048   83  Linux sudo fdisk -l

Disk /dev/sda: 320.1 GB, 320072933376 bytes
5 heads, 63 sectors/track, 1984579 cylinders
Units = cylinders of 315 * 512 = 161280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x135c058f

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           7        1301      203776    7  HPFS/NTFS
/dev/sda2            1301      651462   102400360+   7  HPFS/NTFS
/dev/sda3         1905278     1984571    12488704    7  HPFS/NTFS
/dev/sda4          651463     1905277   197475862+   5  Extended
/dev/sda5          651463     1738212   171163093+  83  Linux
/dev/sda6         1868262     1905277     5829988+  82  Linux swap / Solaris
/dev/sda7         1738213     1868258    20482048   83  Linux

Natty overwrites the existing grub install (maverick's) and afterwards fails to recognize that maverick (on /dev/sda5) exists.

While mount/unmount works:

$ sudo mount /dev/sda5 /mnt
[sudo] password for natty: 
natty@mavericklaptop:~$ mount
/dev/sda7 on / type ext4 (rw,errors=remount-ro,commit=0)
proc on /proc type proc (rw,noexec,nosuid,nodev)
none on /sys type sysfs (rw,noexec,nosuid,nodev)
fusectl on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
none on /dev type devtmpfs (rw,mode=0755)
none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
none on /dev/shm type tmpfs (rw,nosuid,nodev)
none on /var/run type tmpfs (rw,nosuid,mode=0755)
none on /var/lock type tmpfs (rw,noexec,nosuid,nodev)
binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,noexec,nosuid,nodev)
gvfs-fuse-daemon on /home/natty/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=natty)
/dev/sda5 on /mnt type ext4 (rw)
natty@mavericklaptop:~$ sudo umount /dev/sda5
natty@mavericklaptop:~$ mount
/dev/sda7 on / type ext4 (rw,errors=remount-ro,commit=0)
proc on /proc type proc (rw,noexec,nosuid,nodev)
none on /sys type sysfs (rw,noexec,nosuid,nodev)
fusectl on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
none on /dev type devtmpfs (rw,mode=0755)
none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
none on /dev/shm type tmpfs (rw,nosuid,nodev)
none on /var/run type tmpfs (rw,nosuid,mode=0755)
none on /var/lock type tmpfs (rw,noexec,nosuid,nodev)
binfmt_misc on /proc/sys/fs/binfmt_misc type binfmt_misc (rw,noexec,nosuid,nodev)
gvfs-fuse-daemon on /home/natty/.gvfs type fuse.gvfs-fuse-daemon (rw,nosuid,nodev,user=natty)
natty@mavericklaptop:~$ sudo update-grub
Generating grub.cfg ...
Found linux image: /boot/vmlinuz-2.6.38-7-generic
Found initrd image: /boot/initrd.img-2.6.38-7-generic
Found linux image: /boot/vmlinuz-2.6.38-6-generic
Found initrd image: /boot/initrd.img-2.6.38-6-generic
Found memtest86+ image: /boot/memtest86+.bin
Found Windows 7 (loader) on /dev/sda1
Found Windows Recovery Environment (loader) on /dev/sda2
Found Windows Recovery Environment (loader) on /dev/sda3
Found Ubuntu 10.10 (10.10) on /dev/sda5
done

BTW: 
$ sudo fsck /dev/sda5 && sudo update-grub
seems simpler than:
$ sudo mount /dev/sda5 /mnt && sudo umount /dev/sda5 && sudo update-grub

Either way something has to give, as continuing to have to go through contortions every time that natty installs/overwrites/changes grub is growing very tiresome. Next step will be to install grub to it's own partition so that natty can't mess with it at all.