I decided today was a perfect day to attempt framing our guest bathroom mirror. I bought 21 linear feet of moulding at Home Depot and went to town with our mitre box saw. Ryan suggested Liquid Nails to attach the moulding since the pressure from hammering or nail gunning is likely to crack a mirror. He also explained that we should remove the little brackets from the mirror and if the mirror isn't affixed to the wall, to use the liquid nails to attach it.
I did this, only to discover...mold. Umm gross. We quickly took down the mirror and I began cleaning. After much discussion, research, and concern that the mold may be lingering deeper in the drywall, we have decided to cut out the drywall that has the mold on it (it's only a couple of square feet. Even though it looks like it's just on the surface and was probably caused by someone splashing/spraying the top of the mirror and it dripping behind, this is the only way we can be sure that it won't come back. Last thing we need is to put the mirror back up and not know that something's growing back there.