Quoting Craig Sanders (cas@taz.net.au):
i've had it happen on kernel upgrades, and even on reboots - a new version of udev or something loaded modules in a different order, so drives got detected in a different order.
I can envision that happening if your kernel suddenly changed from old drivers/ide SATA drivers to modern libata one - a one-time changeover that occurred sometime early in the 2.6 kernel series, if I remember what I wrote on http://linuxmafia.com/faq/Hardware/sata.html correctly. I envision that happening if you use multiple, different drive technologies (e.g., PATA and SCSI). I have having a difficult time envisioning it happening otherwise. Your master drive on the first PATA chain will always get the first PATA device assignment, your third SCSI device on a SCSI chain will always get the third SCSI device name allocated to that chain, and so on. In short, I suspect that the applicable scenarios are either very rare or involve hardware practices about which the best overall comment is Don't Do That, Then.
i also dislike UUIDs because of their ugliness and non- human-readability so my /etc/fstab has a mixture of LABEL and /dev/md* devices - but i understand how the boot process works well enough to have no difficulty just editing /etc/fstab and whatever else is needed to get my system to boot again if there's ever a problem. i expect you're the same.
This is a good and valid point.
for people without that skill, though, it's better that they just follow the recommended defaults so that they don't cause major problems for themselves.
While recognising that there's a serious cost in lack of simplicity to adopting a method that makes your hardware more difficult to understand and manage, in the name of protecting you from things that are wildly unlikely if you follow elementary good practices in hardware and system management matters. Me, I'd say just keep a live CD around in case of a need to do system maintenance (I like aptosid), know your system, and be prepared to update /etc/fstab in the unlikely event of device names changing - which is highly unlikely to occur except for perfectly obvious reasons that you yourself triggered, e.g., inserting or removing a drive from the middle of a drive chain, or something like that. Or, have it both ways: Keep the UUID rubbish, but move it down to comment lines at the bottom of /etc/fstab, the way I do, and use /dev/sdXX for the functional lines. If you ever have problems, boot that live CD - and you can always swap in the commented-out lines if you can't figure things out otherwise (which I'll bet anyone here can).