I've moved over a dozen times in the last decade and I've had several bummer houses built with plaster walls. Mounting hardware for artwork and mirrors was pricey and unforgiving if my measuring was a little off. I wish I would have known then what I know now. All I needed was a little steel wool!
Steel wool is a magic material in my brain. It plugs mouse holes and keeps intruders at bay, it buffs wood in the final stages of sanding, and cleans rust from all sorts of items. Did you also know you can use it in your walls?
Plaster is tricky and nails are one of its worst enemies. Screws are preferred (so is drilling a pilot hole), but if all you have are nails and you'd really like to hang that piece of artwork without making a trip to the hardware store, try a bit of steel wool instead.
Simply wrap it around the length of the nail tightly, and then hold it against the wall to hammer. It won't give off the same vibrations and rock your plaster the way a regular nail will and will give it a bit of staying power once it's in there.
(Image: Flickr member Naufragio licensed for use by Creative Commons)