A 128MB SDRAM chip just fucked me out of a day's work
I just spent nearly a whole day installing Kubuntu on my second machine. After finally getting the base system to install, I managed to get a halfway working system by installing the rest from the internet (I thought it was a problem with the CD-ROM). Several segfaults and lockups later, I found out the dpkg database was corrupted, so I could no longer install any more packages. I finally said "fuck it", wiped the hard drive, and started up the installation again. After about 5 or 6 times trying to install the base package, I started getting kernel panics. That's when it struck me that it might be bad memory. So, I started Memtest86 from the Kubuntu disk, and it found several locations that were dropping bits. I took the chip out, and Kubuntu installed without a hitch.
So, my lesson for the day is that no matter how stable and robust the OS is, on flaky hardware it's about as stable as Windows 95 is on good hardware.
BTW, if you haven't tried Kubuntu, I highly recommend it. There is a live CD available if you want to try it out before you install it.