Slightly better version here: http://www.ox.ac.uk/media/science_blog/brainboosting.html (includes the link to the actual paper and some others at the end).
One of the concerns they raise is that the required equipment is cheap to obtain or assemble yourself which could lead to unqualified people engaging in potentially dangerous self-experimentation. Soo, any LessWrongers willing to give it a try? ;)
Here looks like a good place.
http://brmlab.cz/project/brain_hacking/tdcs
I'm going to be experimenting with them at the london hackspace so anyone from london is interested, give me a shout,
That ones actually a bit dangerous. The current regulator is rated to go that low, so it's going to be unreliable. In this instance unreliable means brain lesions.
I got excited for a bit, but
http://brmlab.cz/project/brain_hacking
triggered a Google malware alarm in Chrome.
So how does this square with Algernon's Law? (That any simple change that enhances intelligence must be a net evolutionary disadvantage.)
For example, if the treatment makes it easier for a neuron to fire, it also increases the chances of a neuron firing when it's not "supposed" to (because of random noise or whatever).
Evolution hasn't really caught on to the fact that calories are really easy to obtain now, so there's probably some low-hanging fruit available by subverting the brain's energy-conserving mechanisms. (I don't know whether TDCS is doing that.)
I'm not convinced that Algernon's Law is true in general. It might apply to improving intelligence above the currently available range, but it shouldn't apply to raising intelligence within the existing range.
The example of math learning seemed pretty contrived to me. Here is an 8 year old article on transcranial stimulation for drawing. If nothing else, look at the drawings made by the journalist.
The Sydney work is about magnetic stimulation, while the Oxford work is electrical, but the effects sound pretty similar. Electrical techniques are cheaper, but harder to control (2d vs 3d). The drawing article appeared in the New York Times Magazine, but the current web page lacks the drawings.
Article here;
http://www.ox.ac.uk/media/science_blog/brainboosting.html
The article goes on to discuss the ethics of the technique.