Because I was just mailed this:

A new study from AirMagnet has demonstrated that Wi-Fi signal strength can drop by up to 25 per cent when seasonal decorations are in place.
Shiny baubles / tinsel can reflect wireless networking signals, while flashing lights generate all sorts of interference. Sticking to the traditional holly and ivy won't do you any good either, as plants are notorious for blocking the 2.4GHz signal Wi-Fi relies upon.
Carrying out a full wireless survey or network analysis might be overkill, but AirMagnet recommends that signal degradation can often be mitigated just by moving decorations away from access points, and remembering that every barrier between access point and user will lead to a weaker signal.

Anyways, tinsel/baubles/holly/paper chains what do you decorate your abodes with?