Here is a neat photography trick that was part of a challenge from Gizmodo.
This effect and easily be done with a few setting changes. Check out http://www.robertsdonovan.com/?p=702 for some tips.
For the lazy here are the steps;
1.Set your camera to Aperture Priority mode (A or Av on the program dial).
2.Select the smallest possible aperture (f) number for your lens (should be ≤f/4).
3.Switch your camera to manual focus and manually adjust the focus to the closest setting.
4.Zoom your lens to somewhere around 50mm.
5.Find some nice points of light at a distance of 10′ or greater from the camera (your Christmas tree is the perfect subject this time of year).