Let me make it clear that most of the crystal skulls that have been "discovered" have been proven to be man-made objects, as the skull is pronounced with tool marks from humans. However, a select few of these skulls lack any sign of human activity, and some are dated back as far as 36,000 years ago.
The skulls that have been dated and have not been found to have been made by humans are said to hold magical or healing powers. That part is a matter of opinion, as nothing of the sort has been proven. However, in the documentary entitled "Mystery of the Crystal Skulls," a woman claims that people who are ill or inflicted by various physical issues go to her skull (one of the few without human marks) and are healed. The only two things that I find endlessly interesting are the following:
1. If a laser is shone in a specific placement and orientation towards any of the true skulls, they cause the beam to become incredibly powerful through the skull's eyes. I do not know if it is only the eyes, but that is what I remember.
2. This interests me more than the first: The anatomy of the true crystal skulls is identical to the anatomy of a human skull.
If these points interest you, research the "Mitchell-Hedges" skull, which is the most famous and best portrays the fore-mentioned characteristics. (This skull actually resides in Canada)
To see an interesting article concerning the origin, etc. of the crystal skulls, click here. The most interesting part that I found is the following (from the article in the link):
The Mitchell-Hedges family loaned the skull to Hewlett-Packard Laboratories for extensive study in 1970. Art restorer Frank Dorland oversaw the testing at the Santa Clara, California, computer equipment manufacturer, a leading facility for crystal research. The HP examinations yielded some startling results.
Researchers found that the skull had been carved against the natural axis of the crystal. Modern crystal sculptors always take into account the axis, or orientation of the crystal's molecular symmetry, because if they carve "against the grain," the piece is bound to shatter -- even with the use of lasers and other high-tech cutting methods.
To compound the strangeness, HP could find no microscopic scratches on the crystal which would indicate it had been carved with metal instruments. Dorland's best hypothesis for the skull's construction is that it was roughly hewn out with diamonds, and then the detail work was meticulously done with a gentle solution of silicon sand and water. The exhausting job -- assuming it could possibly be done in this way -- would have required man-hours adding up to 300 years to complete.
Under these circumstances, experts believe that successfully crafting a shape as complex as the Mitchell-Hedges skull is impossible; as one HP researcher is said to have remarked, "The damned thing simply shouldn't be."
The connection between the skulls and the prediction of the world ending in 2012 SEEMS to be that the skulls were given to the Mayans by the gods or by some higher power, and that they helped to stabalize or control in some way the earth's rotational pattern. The legend, it appears, states that the crystal skulls must all be found and brought together on December 21, 2012 (the day that the Mayan's predicted as the world's end) in order to stop the world from unstoppable destruction. This is the only explanation that I remember finding, but I know that it is much more elaborate than I have presented it. I think it is a topic worth researching on your own.
The only other thing I figure is worth addressing at the moment is that crystal skulls are said to be able to hold vast amounts of knowledge, both from the past and from the future. Although I have not researched much on this part of the legend, I do know that Quartz crystal (from which the skulls are made) is, in fact, actually able to hold information, and is actually what is used (on miniscule scales) in computer chips. That is all I know about that part.
I also think that the documentary is worth looking for, whether on the internet or on DVD - very interesting.
