Agreed. I'd also argue that the "cuteness" of such an error page actually can have a major impact on how much the visitor will forgive you. Twitter's Fail Whale is the perfect example :)
Anything is better than Borders' page (except possibly a blank one)... even a rather cold, drab, boring error page that at least describes the error (we are over capacity, sod off) would serve better. I don't think we really need to do any extensive focus group testing to agree on this much...
