Chris_R - 10:31 pm on Jan 4, 2011 (gmt 0)
Sometimes they show up as unavailable for me as well.
I am not saying google isn't incompetent, but just that there could be a logical reason for this. If you read over their papers and such - they don't claim to store all this data all the time. They might decide to crawl you for one reason or another - and then delete that link from their set.