A recent update of Archlinux moved all binaries to /usr/bin. The update was smooth on my main system, but for my 4 years old virtual Arch, a 'pacman -Qqo /bin /sbin /usr/sbin | pacman -Qm -' revealed that grub 0.97 required a fix.
I could have installed grub-legacy from the AUR, but that idea struck me as a rather backwardish one. Since I learned to really like syslinux from my main system, I installed this modern bootloader instead. Upon a reboot I was greeted with "no operating system found". Hm.
I soon learned that the problem originated from the fact that my /boot partition starts with sector 1. Well, just like fdisk partitioned a few years ago. Now, I could have converted the partition to GPT, but I didn't like that idea too much either. Instead, I tried grub2, only to get rebuffed once more: "no post-MBR gap; embedding won't be possible". Aarghhh!
Finally, it was the Gentoo Wiki which told me what to do: "If you really want blocklists, use --force." A 'grub-install /dev/sda --force' later, my virtual Arch is up-to-date and thus again as new and shiny as in the beginning.