Even if it were possible to switch manufacturing to the US.... can you even conceive of what a ten-fold to 20-fold increase in labor cost would do to the retail pricing of a Mac Book Pro?
Apple certainly has big enough margins to manufacture their products in the US without needing to dramatically hike their prices. But obviously shareholders wouldn't like it one bit. And Apple has a legal responsibility to put their shareholders interests above pretty much anything else. So it cannot and will not happen.
There was a really good report recently that highlighted Apple as an example of how this could actually be done - on numbers anyway. Not only would it be great for employment, but if more companies began doing this, the trade deficit (import) with China would obviously reduce, and effectively plough more money into the US economy. Win-Win for US.
The example used was an iPhone, which costs around $6 in labour to assemble in China (around $160-180 in parts I think). US labour costs are around 10x more, so that would make the cost to produce it around $60.
However, it's anticipated that Apple could refine this figure and absorb the cost, and get significant tax breaks were they to manufacture in the US. I would also happily pay a little more if I knew the products weren't made in a posh sweatshop.
Long term, the Chinese population's rapidly increasing standard of living, the [relative] malaise of the US economy and, very long term, China taking over the world and hoarding their own resources (while the rest of the world sells them their's for cheap) is going to make the concept of bringing manufacturing back to the US much more viable and actually desirable, but it still won't be easy.
One issue for Apple specifically is you can imagine how hard it would be to keep secrets in the US, given the 1 million employees would not be fenced in in their compound.
Personally I would like to see Apple invest some of the $60 billion in cash it holds into doing something significant like bringing manufacturing home. A massive corporate initiative, and thinking of home first would be a brilliant way to breath some life back into the US as a country, and as an economy.