They even gave me a nice picturehookythingummy.
I therefore drove the nail into the wall, with the picturehookythingummy on it.
Put the picture on the hook.
Let go of it, to lean back and see if I had it straight.
And then leaned back Very Very VERY fast, to grab the damn thing that had completely outweighed the picturehookythingummy's tolerances and bent it out of true, so I could stop it 2" down the wall as opposed to letting it slam into the stereo.
So now I have driven three nails into the wall to hold the frigging thing up and I'm still edgy about it falling and the glass shattering, and having to go through finding the stupid thing all over again.
Edgy enough about it that I put two softish things where it would hit the stereo, so as to cushion any fall and hopefully keep the glass from shattering. If it does fall. Which it might, you know. Any minute. Gah.
Me? Paranoid? Naaaaaaah.
UPDATE: next day, I put it on a picture hook. It hangs a bit higher than I'd like, but I'm not worrying about it like crazy.