karen - I suppose it depends on what you sell. I sell jewelry and it has been my experience that women will browse in jewelry pages and buy at any time of the year. It may slow down a bit at Christmas because folks are busy and/or away but there are always shoppers.
As for things not arriving in time for Christmas....unless your customer specifies that this purchase is a gift, what are you worried about? I have seen a few seller's TOS that offer courier services for those who want their items before a certain date. Of course this will be at the buyer's expense. So, you could even add that to your OWN auction page. Tell your winning bidder to let you know if he/she needs the item in a hurry. It's getting to the point now where most people won't dare expect something before Christmas, expecially if it is an International sale.
Lots of luck,
Jackie...