I am using Ubuntu for a long time now. Beginning with (I think) Maverick Meercat I can see a peculiar behavior. My desktop system has three physical disk drives (100GB, 250GB and 2TB).

Before Meercat these physical disks were reliably assigned to these devices:
100GB disk -> sda
250GB disk -> sdb
2TB disk -> sdc

And beginning with Meercat this assignment is somewhat random. Sometimes I get the above assignment after a reboot but sometimes it is this way:
100GB disk -> sdc
250GB disk -> sda
2TB disk -> sdb

The 2TB drive is a SATA drive while the other disks are IDE drives.

After each reboot there seems to be a 50/50 chance
for one or the other drive-to-device assignment.

Has anybody else observed such behavior?

Hi, I had this some time ago (not Ubuntu) and it appeared to be related to the UUID of the disks... or (in fact) the NON-use of UUID in my fstab at the time. So, are you saying (for example) that partitions on sda are being mounted incorrectly - because sda is no longer the physical 100GB drive?
I had an IDE (Pata) as my first (boot) drive and some other Sata drives as secondary. SOMETIMES they would "swap identities".
It related to a USB stick that I had stuck in the machine at boot time. The "smart" bios was moving things around.
So.... (if I am close) I would suggest ensuring that you use UUID's for all devices - rather than "sda1, sdb3" etc.
Dave