I asked a question in this forum an hour ago:

http://serverfault.com/questions/352914/odd-entries-in-dns-lookup-log

The question contained the string "xdnrhkbqnn".  If I now Google this string I get just one hit, namely my question.  

How did Google get to index this page so quickly. Is there a way in which Serverfault.com gets pages indexed quickly?