Eggshells for what?

Once again browsing my usual blogs this morning (the way I start my days when I'm off and nursing a cup of joe), I found an interesting post on ways to re-use eggshells on Re-Nest.com. I've always been curious to their potential as I throw the delicate little shells in the trash as I bake or prepare one of our egg, pancake and bacon breakfasts. Here are 8 ways to use these shells around the house. Some I would never have thought. In particular I was shocked by the coffee suggestion...putting eggshells in my coffee grounds, ha!?! I consider my self a coffee aficionado so never having heard of this tradition/technique I decided to explore further. Eggshells are a tactic for "cowboy coffee" so let's just say, I won't be changing my coffee-making habits. Read after the jump for what I found; otherwise keep reading here for the re-uses of eggshells.

1. Finely crushed, they help keep your drain clear.
2. Eggshells in the garden have many uses. Moderately crushed shells placed around your plants discourage cats from using your garden as a potty and they also keep slugs away. Mixed into the soil that surrounds tomato or pepper plants, they're an excellent fertilizer.
3. To remove stains from a tea pot, thermos or water bottle, fill it with a mixture of crushed egg shells and a little bit of water, shake vigorously and let sit overnight. You can also use the same technique in your kitchen or bathroom sink.
4. Crushed eggshells added to a greasy pan helps remove stuck or baked on food.
5. Don't toss the water that the shells have been sitting in. Use it to water your plants. 
6. Use a half shell for starting seedlings. It not only makes a great container but the calcium carbonate in the shell provides the growing plant with some extra nutrition. Break eggs so that you have about two-thirds of the bottom part of the shell in tact. Rinse out. Poke a hole in the bottom with a pushpin. Fill each egg with some soil, and plant a few seeds in each egg. Place eggs back in the carton. Once the seeds are big enough to plant, put them into the ground, shells and all. The shells will act as fertilizer.
7. Mix crushed eggshells with your coffee grounds for smooth coffee. The calcium in the eggshell helps to reduce the acidity of coffee and will also help any loose grounds sink to the bottom of the cup.
8. Dry them out by placing in a low oven for a half hour. Crush them finely and add them to your dog's food for a boost of calcium.Why do some people put eggshells in coffee grounds?
   Here is what I found...This is bit of folklore that has been explained in at least two different ways. Some old cookbooks claim that the eggshells help to clear the coffee by attracting floating grounds and then precipitating to the bottom; some of these old recipes call for adding an entire raw egg. Less commonly, adding eggshell to the grounds of coffee is said to reduce bitterness (though improving the coffee to begin with would be a better tactic.
   The tradition was to use rinsed eggshells, which largely throws out the supposition that it is some component of residual white or yolk that is the active component. The shell is composed almost entirely of calcium carbonate, with the remainder consisting of magnesium carbonate, calcium phosphate, and some miscellaneous organic matter. The only possible effect could be to raise the coffee's already relatively neutral pH; it is unclear whether any change in acidity, assuming one even occurs, would be detectable by taste. Regarding settling the grounds, how the addition of large pieces of a mineral could settle coffee grounds is, at best, unclear.The calcium compounds in the shells would likely neutralize a small portion of the acids. Naturally, if you crush the shells more, there's more surface area to react, and slightly more neutralization. Avoid decaf, unless it's by water process! They extract the caffeine with dichloromethane (or methylene chloride as it's also known) which is a known carcinogen. But then, why drink decaf? Don't we all love our Vitamin C? (C for caffeine... )