Well, the general rule of thumb is that DLR starts trotting out the Christmas decorations and putting them up as soon as Halloweentime is over. So, in 2009, Halloweentime ended on November 1. I would guess that the beginnings of the Christmas stuff started to go up on 11/2, and then it continues for the next couple of weeks, with more and more things being added each day.
Now as for the "official" start of Christmastime at DLR, last year it began on the Friday 2 weeks before Thanksgiving, but in 2008 and 2007, it began on the Friday one week before Thanksgiving. Not sure what they will do this year. The reason why the "official" start date is important is because that is when certain things commence, i.e. Santa's appearance in several places around DLR, the 'snow' on Main Street, the lighted Winter Castle (it has 'icicles' that light up at night and there is a little light "show" that extends from the castle up Main Street to the giant tree), carolers strolling around the Resort, the official opening of IASW Holiday (though that could have a soft open a couple of days early), any other special holiday fireworks and entertainment, etc. The seasonal food, music and merchandise all begin before the "official" start date.
Yes, you must visit DLR at Christmastime. I have spoken to people who have been to WDW during the holidays, and while they all agree that it is spectacular, the ones who have also been to DLR at that time of year all agree that DLR holds its own in the holiday department! Even if there were no holiday overlays of rides (IASW Holiday and Haunted Mansion Holiday), it would still be charming, magical and enchanting. In fact, I fell in love with Disneyland at Christmastime even before there was a DCA, before there was a GCH, before there was snow on Main Street, before there was a Winter Castle with sparkly icicles at night, before there was an IASWH or HMH - but now all of those things added into the mix have just enhanced my love of DLR at Christmas 500% (at least)!!!
