Earthquake at Apple! Steve jobs left. It's always a nightmare for big companies when they see their charismatic CEO leave. The success of Apple was really connected with the image of their CEO.
You might know that Jobs already left Apple in 1984. As a results Apple's sales went down and they had to buy Jobs's new company (NeXT) in order to retrieve their CEO and therefore their success.
But this time, things are going to be different. As he mentioned on his resignation letter, Jobs is going to stay as chairman in Apple's board. I don't see Jobs resignation as a real threat to the company. I'm positive his leaving has been fully prepared and I suspect Apple will release a huge piece of news in order to prevent a drop of its shares.