I've seen this technique posted quite a few times around the web, so with the christmas tree up I decided to try out taking photos of pinpoints of light out of focus through a cut-out stencil. I made a tube to fit over my 50mm 1.4 Canon lens that included a small holder at the end into which I could slide pieces of cardstock that I'd punched or cut shapes out of. The slips of cardstock resembled slides, with a cut-out at one end. I made a snowflake and star cut-out using a paper punch tool I bought at a craft store, then I cut out a smiley face from a third strip using an x-acto knife. Below are the results:
Having the stencil about an inch from the end of the lens adds a nice dark vignette to the photo - none of these were touched, they came straight from the camera with the exception of a little exposure tweak on the smiley face shot which was also cropped a bit.
The star and smiley face were shot at 1/30th second and the snowflake was shot at 1/60th, all three were shot with the 50mm 1.4 at f/2 and ISO 1600 (it was pretty dark in there). I tried some outside shots, but it was damn cold out so I bagged after just a couple frames. I want to try this again maybe as I'm putting away the lights so that I can have a foreground subject in focus and throw the background lights out of focus to create the effect.