Got a Wii? Got A Christmas tree with lights? Got them next to each other?
Yeah, you might want to move them, if you haven't wised up and done so already.
The blinking and flickering of Christmas tree lights plays havoc with the Wii Remote and sensor bar, causing all kinds of problems. BBPS has a few reports up, and I've seen it personally at a mate's place as well; the cursor jumps all over the place and your connection keeps dropping out, and occasionally the Wii won't detect the Remote at all.
While this is an annoyance to anyone with a small apartment who can't move their tree and/or Wii, for others this should be an opportunity. A gold star to the first person who can rig up their Christmas tree's light sequencing so it can kick someboy's ass at Wii Tennis.