Since I work with Macs, and the multi-core powermacs make most sense to me how far you should go with "personal computers", when a friend of mine told me that he was in a possession of a Cray CX1, I was not impressed.
It's some special-Windows-driven graphic workstation that he can't really take advantage of (how he got it is sort of a personal story... but he got it straight from Microsoft). You will hear the word "cray" whispered in a scientific or academic environment maybe, but not on your train to work.
It's a "personal" computer, i.e. when you plug it in, supposedly the lights will still be up in your building. We don't know, because the gigaflop-chewing monster has been gathering dust for almost a year. I think nobody was interested in the ads he posted.