There can now be little doubt that Apple shareholders, not to mention the company's legendarily loyal customers, have to prepare for a world without its driving force.

News that Steve Jobs has resigned as chief executive is surely something investors have been dreading since his January decision to go on medical leave. While he is staying on as chairman, Mr. Jobs' statement that the 'day has come' when he can 'no longer meet my duties and expectations as Apple's CEO' can only confirm the worst fears about his health.

The challenge is assessing the long-term impact. While clearly Apple's momentum isn't likely to suffer in the near term