We always use the hollow wall anchors. They work great, and they don't have to be in a stud.

I too am curious why it says not to use wire. If done properly, I would think it would work quite well. That is if you want your mirror to hang angled downward. If it's triangle loops aren't sturdy enough to work with wire then they shouldn't be able to hold the mirror any other way either. At least in my opinion.
We have two large, but not quite so heavy mirrors that we'll be adding the same sort of "loops" to the frame. We've had great luck with use the drywall anchors that look like large plastic screws that you screw into the wall first. They come with screws that you then screw inside the plastic anchors leaving just enough stuck out of the wall to attach the "loops" over.

Here is a link that might be useful: The item shown in the back is what I'm talking about. The ones we have are white though.

I guess I never trust those hollow drywall hangers even though I'm sure they work. I'm thinking the mirror company doesn't want to be held liable if you use a wire and the mirror's weight/tilt causes it to come off the wall...especially if you are just hanging the wire on the screw heads (which I wasn't planning on doing).

bigdoglover, what exactly is a picture hanger? I'm assuming it screws into the drywall, but is it just a screw or does it have a hook shape that lets you hang the mirror hoops on?

Robin and Justgotabme, did you just hang the mirror hoops right on the drywal screw heads? I would think that would be even more likely to fall than using a wire on hooks screwed into the studs. Or did you use the drywall screws to attach some sort of hooks to the wall and then hang the mirror hoops on those hooks?

Thanks again people!

I would use a cleat.

I would NOT use wire. If your mirror is very heavy, as you describe, you will be concentrating the weight at a single point in the middle of the wire. This is not over or even near the two anchor points for the wire (the triangular hoops), and thus if the conditions are right it will pull out of the wall.

We recently had a 20 lb mirror hung by the handyman I get for such jobs. He used something called a "molly" and put two of them in the wall. The two triangular hooks hang on them. Something that heavy needs to have more than one attachment, to spread out the weight.

We were planning on hanging the wire on two wall hooks to distribute the weight.

What is a cleat or a molly?

Cleat?
http://www.govart.com/images/hwr_cleat-lt-demo1LG.jpg

Molly?
http://z.about.com/d/homerepair/1/0/7/4/-/-/toggle_molly.jpg

Were they attached to studs or, as in the second picture, were they using hollow drywall type screws?

Yep, that's a cleat and a molly!

Cleats are nice because the weight is distributed across its length. VERY sturdy!

IF the mirror is large enough, I'd put the cleat onto the studs.
If not, I'd use molly bolts. But, if at all possible, I would try to get at least ONE side of the cleat onto a stud.

How informative!

So if I use molly bolts, I'm assuming I can just line them up with, and hang the mirror hoops directly onto the bolt heads?

If I use cleats, it would seem that I need to use a wire in order to lay in the cleat track?

I'm almost there.

No I think molly's are like these

http://www.naturalhandyman.com/iip/inffastener/i/molly1.jpg

The ones in your picture are toggle bolts, one draw back is that they are not as precise, and seem to require tightening down for it to work, so there won't be a bolt stick out for you to hang with, unless you use that to secure a cleat or bracket.

I used 2 hollow wall anchors (molly) like above picture, but as a fail safe, I also strung a 100 lb rated wire between the two, onto a earth quake proof hook in the center (it's got a maze for the wire so it's hard to come off), the wire is not under tension, it's just incase an anchor fails it will not fall into the ground. That hook is fastened into a stud with a 3" screw and rated for 100 lbs. Of course everything is still at the mercy of the hook on the back of the mirror though.

Where I live, at home depot they have a earth quake area that sells the hooks and muesum wax, cabinet brackets etc, that's where I get the hook with the maze in it.

I just hung our heavy mirror and found that the problem with the wire was that when I attached it the way I usually do like on a framed picture, the weight of the mirror pulled the wire so taught it eventually slipped. I think I solved the problem by wrapping the wire around the triangular hoops a few times then knotting it and then wrapping it around itself. I also strung two wires - just in case.

I really like the suggestions of using two hooks to distribute the weight. I think I will take it down and add the two hooks.