Ok, they're not really perpetual motion machines, but their continued improvement certainly looks like one. Take a look at this graph from the group that rates the top 500 supercomputers:

It's almost a perfect exponential growth! At this rate, when I'm 50 and super rich I might buy the 500th fastest supercomputer running at 1 ZETAFLOP! At the same time, SI will be scrambling to make up more Star Trek like names because the #1 supercomputer will already be at a Yottaflop, and Wikipedia doesn't have any more names.
Yes, I had to look those up - which makes this even more ridiculous.