But when I read the article, I realized it was legit. Researchers from the UK were using gene therapy to treat cancer cells, but were having difficulty getting enough of the monocytes localized to the tumors. Monocytes are a form of immune cells, but in this case they are being used as a carrier for genes that are meant to aid in the fight of cancer. The researchers overcame the problem by loading the monocytes with ferromagnetic nano-particles. They were then able to sequester the therapeutic monocytes to the tumor by holding a magnet over it (results to be published in the journal Gene Therapy in June).
It's unlikely that the magnet is strong enough to actually pull the particles from other parts of the body to the problem area, but they probably flow around the body in the bloodstream, and the magnet concentrates the particle-containing cells in one place. It's like panning for gold with a sieve, only the magnet is the sieve for magnetic particles. There's a long way to go before something like this is proven to be safe and effective in humans (the article didn't say which model organism they used, but it was probably done in mice), but the idea is so cool I just had to write about it.
If you're worried about how a magnet might affect your blood, always remember that the iron in your blood cells is non-ferromagnetic, meaning it has no magnetic properties. So it should be safe, at least based on what we know now.