When I was served with the summons on October 1,2009 and had 30 days to reponse, when is the last day to response?

Monday, November 2, 2009.  Thirty days from October 1, 2009 was October 31, 2009, but since that was a Saturday, the deadline is the next business day.  However, that is the day the papers have to be received by the court, not the day to mail them.

If you missed the deadline, you need to respond as quickly as possible.  A very short delay is almost always not a serious problem.  But, the longer you wait, the more complicated the process becomes.