AAAAAUGH!
We also received interview letter yesterday, scheduled for Aug 27, but we have already purchased tickets to travel to a wedding out of state over that weekend and are going to have to reschedule. It is literally the only thing on our summer calendar that we couldn't move or skip for sake of the interview, what rotten luck. I guess we shall see how much of a delay this creates for us... we sent the letter back today requesting a reschedule.
04/01/09: priority date
04/28/09: FP notice
05/07/09: FP
06/22/09: CFR (yellow letter)
06/24/09: Interview letter
08/27/09: Interview scheduled (pending reschedule)