[Warning: extreme geekiness ahead! Non-geeks might want to skip over this post and look at the pretty ponies instead.]
I figured out what was causing my home Linux server to think it was busy. It turns out my server has an automounted nfs share from another server, a server which happened to be down. I’d done a few df commands to check disk space before I downloaded the new Ubuntu release and these commands hung in uninterruptible sleep while they waited for the drive share that would never be found.
A few of the updatedb cron jobs also piled up when they couldn’t reach the share. Though these processes weren’t using the cpu they were still affecting the load measurements. When I rebooted the server today the load had climbed up to 19, which is usually a level at which your computer is comatose though in this case mine was still quite responsive.
Bottom line: autofs can trip you up in unexpected ways. Now back to the ponies!