I still use my server, that is basically a self-made NAS additionally used for irc that's always online (via irssi and screen) large over-night downloads (so I don't have to keep my energy-hungry main pc turned on). I occasionally use it to test out some Linux-stuff (like testing C++-code on different versions of GCC), too.
The server houses 6 SATA drives that are all members of a software-RAID5 and one IDE hard-disk I keep the OS on (previously Debian). I did not want to install the OS on the RAID, because I wanted it to store data only. Since I had bad experience with HDDs in general and IDE-disks especially, this one IDE drive was always something I wanted to replace. Unfortunately, all SATA ports of the motherboard and the additional Adaptec controller are already in use, so I had to stick with the IDE port.
Recently I could not access this box anymore and when I hooked up a monitor to check out what's wrong with it, the console was filled with i/o errors on hda. "Now is the time to replace that last piece of possible failure", I said to myself. A reboot brought no failures, though, and till today I still think the disk is okay and it was a software-failure, but I still wanted to replace the drive with an USB-stick. I had read about booting from USB before and already had an USB-stick with an Ubuntu Live-CD on it. So I ordered another one to use as the OS's root drive. Well actually I used the stick I already had and replaced it's day-to-day usage with the new one, since it was smaller and looked nicer. I did not want to boot a Live-CD, but actually install Ubuntu on the stick, though. When I googled for "Ubuntu USB install" or similar keywords, I always ended up with a Live-CD or a read-only root, and even that took quite a tedious process. But then I stumbled upon this tutorial that made clear the obvious: You can simply put in your Ubuntu CD and your USB stick and install to it like you would to any other drive. Damn! It was so easy :-) The only caveat, as mentioned in the tutorial, is that on the last step of the installation you have to explicitly choose the USB-stick as the boot-device. By the way, it's freaking neat to be able to manually select the boot-device! And on another side-note, the new Ubuntu installer itself is pretty neat, too. It's easy, even not so tech-savvy people could use it without problems. So I burned Ubuntu 9.04 to a CD, booted from it on my main PC (since the server does not have a CD-ROM), plugged in the USB-stick and installed Ubuntu on it. Then I plugged it into the server, did some last fiddling with the settings, copied over the content of the IDE-disk to a backup-directory on the RAID, turned the system off again and unplugged the IDE-disk.
It all worked pretty well, except that the device's name of the USB-stick changed after unplugging the hard-drive. I only had to manually edit GRUB's boot-command (that is another feature that has saved me hours of fiddling already) and later edit it's default configuration. I just guessed that sdh1 has become sdg1, which wasn't too difficult. :-)
Finally! A completely IDE-less system! And additionally, I have minimized the risk of data-loss, because I'd suspect the chances of a head-crash on an USB-drive to be pretty low. Sure, flash-memory wears off after time, but I hope that time-span is much larger than the durability of a hard-disk.