Apple is set to report earnings today, and analysts are expecting revenue to jump to as much as $24 billion, a rise of 55 percent over the year-ago quarter. But the thought of the company without Steve Jopbs is casting a pall over the good news.

Earnings estimates are similarly lofty, with the averages coming in at $5.38 per share, well above Apple's own guidance issued in October, which was $4.80.

The iPhone and the iPad are two big reasons for the optimism. Both were must-have products this year, and even though iPhones were still locked to one carrier, AT&T, in the U.S., sales were brisk with Apple saying it sold 14.1 million iPhones in the first three quarters of 2010. The addition of Verizon will likely increase sales, even when the users that defect from AT&T are taken into account.

But the upbeat mood at the earnings call will be tempered by concerns over Steve Jobs' health. Jobs has taken leave for health reasons three times in the last 10 years and Apple has survived and even thrived. But there is no doubting that his vision has gone a long way towards shaping the design decisions that have made Apple products so unique.

In his public appearances, Jobs has never been shy about articulating his vision, and even defended it on occasions when it didn't work as planned. Famously, he made a rare apology for the antenna problems that beset the iPhone 4. During the third quarter earnings conference call, Jobs attacked rival tablet makers' idea that a 7-inch tablet would sell, calling such tablets DOA. He also criticized the Android operating system, saying that Apple's integrated approach was better for users.

As importantly, Apple went into one of its more turbulent eras after Steve Jobs was fired in 1985. Apple performed well for a while, but ran into problems towards the 1990s. Jobs went on to found NeXT, which was subsequently bought by Apple itself, bringing him back in 1996.

Some analysts have questioned whether Apple can keep up its blockbuster performance without Jobs. Brian Marshall of Gleacher & Company put a floor of $300 on the stock.

There are others besides Jobs who could have a say in the company's direction. Chief Operating Officer Tim Cook, will be acting CEO in Jobs' absence, and there is Jonathan Ive, senior vice president of industrial design who is largely responsible for the look of Apple's gadgets. There are also people such as Philip Schiller, senior vice president of product marketing and Eddy Cue, vice president of Internet services.

Jobs was not clear what the problem was that is causing him to take a leave, but he has been battling pancreatic cancer for several years and in 2009 had a liver transplant.

Apple may ride the wave of the iPad and iPhone for some time, as there are product upgrades schedule for the first quarter and Apple usually has regularly scheduled launches of new versions. While it is difficult to imagine Apple without Jobs, the company may be forced to do so soon.