It has been no secret TSMC -- the world's largest dedicated independent semiconductor foundry -- has not been able to deliver when it comes to producing high yields for their latest 28nm parts.
This shortage, though affecting other companies, is predominately hurting AMD and Nvidia, as neither company can ship their latest 28nm graphics cards in high-volume. In the case of Nvidia, it has caused them to delay the launch of more 28nm models. What this means for you is it could be some time before the GTX 680 becomes readily available and for AMD to reduce the prices of their Southern Islands graphics line to Kepler prices.
The good news is production is expected to pick up in Q3 2012, at which point we should see a dramatic increase is the volume of both AMD and Nvidia products.