Mirrors are almost as effective in the RF spectrum as they are in the visible spectrum.
UPS's tend to have all kinds of transformers and rectifiers inside of them that can (especially on cheap models, the more expensive models are a whole different bag of worms [Not that they can't also cause problems]) spit out interference on more or less any frequency.
While your at it your cable or DSL modem is doing the same thing.
As well as anything that contains water, water is the bane of 2.4 Ghz.
My personal favorites for anecdotes involving RF interference and shielding are fishtanks and beer kegs.
Oh and don't forget people, we are how many percent water again?
Though I have also heard stories where a person's wireless only worked when they face one way because they themselves were too much shielding.