Something that has become more popular recently is magnet therapy, these quantumly aligned materials have shown up in everything from bracelets to insoles and woolen underlays. The usual claims are for easing joint pain but also include increasing blood flow as well as blood oxygen levels, there is even at least one company claiming a magnetic cure for cancer. Once again this is a case of the claims far out running the evidence which should back them up. While there have been a few preliminary studies which show benefit from magnet therapy there is an enormous difficulty in properly blinding studies, who can doubt they are receiving the real deal when it sticks to their keys?
The most popular explanation of the efficacy of magnets is the appeal to the fact that there is iron in our blood. Unfortunately this iron is non-ferromagnetic, it just does not respond to the magnetic field the way a solid iron bar would. Even if the iron in our bodies did respond to a magnetic field there is no reason to think that this would be a positive thing. Imagine magnetic insoles that pulled your blood into your feet, or a mattress that impeded the blood flowing around your body. These are the sorts of effects that would be expected of a physical interaction with a magnetic field, not a magical healing power.
While magnets do admittedly have very unusual properties and wrapping your mind around how they can affect materials from a distance is difficult, the leap to them being a panacea for whatever ails you is not warranted. Finally, if there were any validity to these claims I suspect the use of MRI machines would be significantly messier.