Comment 6 for bug 514485

Reinstalled Kubuntu 9.10. Problem hasn't reappeared yet, even after using USB stick on a windows machine before.

Just in case it's useful, here's a diff of fstab+mtab before and after reinstallation:
=======================
[~/kernel_hangs/diff]$ diff fstab_before fstab_after
3,5c3,5
< # Use 'vol_id --uuid' to print the universally unique identifier for a
< # device; this may be used with UUID= as a more robust way to name devices
< # that works even if disks are added and removed. See fstab(5).
---
> # Use 'blkid -o value -s UUID' to print the universally unique identifier
> # for a device; this may be used with UUID= as a more robust way to name
> # devices that works even if disks are added and removed. See fstab(5).
10c10
< UUID=c33b4bf0-bf60-455e-bb7c-2c3c499582d3 / ext4 relatime,errors=remount-ro 0 1
---
> UUID=0a03bba2-be0c-4f77-a393-dd39ff775ea9 / ext4 errors=remount-ro 0 1
12c12
< UUID=75eb4ad5-320f-4c6a-ae11-d0237997d55a /home ext4 relatime 0 2
---
> UUID=75eb4ad5-320f-4c6a-ae11-d0237997d55a /home ext4 defaults 0 2
[~/kernel_hangs/diff]$ diff mtab_before mtab_after_nousb
1c1
< /dev/sda2 / ext4 rw,relatime,errors=remount-ro 0 0
---
> /dev/sda2 / ext4 rw,errors=remount-ro 0 0
13c13,14
< /dev/sda5 /home ext4 rw,relatime 0 0
---
> none /var/lib/ureadahead/debugfs debugfs rw 0 0
> /dev/sda5 /home ext4 rw 0 0
=======================

mtab after plugging in the USB stick:
=======================
[~/kernel_hangs/diff]$ diff mtab_after_nousb mtab_after_usb
15a16
> /dev/sdb1 /media/disk vfat rw,nosuid,nodev,uhelper=hal,uid=1000,utf8,shortname=mixed,flush 0 0
=======================