I just bought in to DVC at the end of September ... I have to admit I did spend a moment thinking "so how much more could I have saved if I had held off two weeks longer" - but the exchange rate I got in September was decent, so I'm not dwelling on it.
That said, if the dollar continues to do well, I'll be stocking up the US savings account to cover dues for the next few years!
One of my "hmmm's" about buying in was that DVC is "foreign" real estate for Canadians ... and who knows what the CAD or USD will do down the road. Hence my plan to buy and save US$ whenever the rates are good.