I went to take my 70-291 yesterday and the Prometric testing software was down at the testing center before I got there (the center's Pearson VUE software worked fine). After waiting for an hour for the admin to resolve the issue, we (there were 7 of us waiting to take a test) were asked to call on Monday to reschedule for free.
I was so not surprised because same thing happened to me a month ago.