Though, like most new things that come up in neuroscience, it gets over-hyped especially in the popular press, there is evidence that it has some effects. So far, the effects found have been rather limited, and we don't know how long they last. But it is not quackery.

However, I would not recommend DIY - certainly until more is known about the side effects.

I have looked at a few of the papers available for public review, and the one thing that stands out for me is that they all seem to agree without further examination that electrodes placed at various spots on the forehead will result in a current path downward through the skin layer, skull, cerebrospinal fluid, dura, into and across the targeted brain area and back up through skull and scalp to complete the circuit. Anyone who is familiar with Ohm's Law can tell you that current will take the path of least resistance, which in this case would be across the scalp between the leads. Bone is not generally a good electrical conductor unless driven by very high voltage (see: Old Sparky). While some current can travel through higher resistances in a parallel circuit, the amount in this case would be exceedingly tiny, likely in the nano-Amps.

It is conceivable to me that such units using electromagnetic fields, rather than current, may have some effectiveness. And in fact, such technology also exists. The tDCS unit described in the latest Wired column uses just a 9V battery and a voltage regulator configured as a current regulator. It simply isn't within reason for anyone with an electronics education to believe the claims that it will perform as advertised.