I would agree with QuiltE that some Christmas cakes are awful - usually due to being too dry, either because they are commercially made (and hence stored for eons before you eat it) or even homemade if the cake is not 'fed' (i.e. painted with brandy - or the spirit of your choice - over several weeks prior to eating)
MrsM - there is a whole mystique about Christmas cake (or heavy fruitcake) actually improving the longer it is left - hence the traditional making it several weeks prior to Christmas Day to allow the flavours to mellow and blend. There is also a tradition here of the top layer of a wedding cake being made to essentially the same recipe and then kept for use at the christening of the couple's first child. Not sure I fancy that, but it gives you the general idea!!
Tartan - I think that traditionally the stir and make a wish is in relation to Christmas pudding (similar recipe but different 'category' of food in that it is usually served with cream or brandy butter as the dessert at the Christmas meal - Christmas cake is eaten as cake at any time around Christmas). Though I see no reason why not make a wish over the cake as well!
I'll dig out the recipe I'm using and post it tomorrow - they do have quite a lot of ingredients though, so be warned! LOL
