If you haven't tripped over an eager Apple fan stationed on the sidewalk outside of a store yet today, you'll still have noticed a certain percentage of pedestrian traffic staring at their iPhones with more avidity than usual. That's because these individuals - whom you will have to swerve to avoid walking into- were probably among the nearly 4 million people worldwide that are expected to purchase an iPhone 4S this weekend.

Many analysts estimate that opening weekend sales of the iPhone 4S will lap those of the iPhone 4, which sold 1.7 million units from June 24-26 in 2010. Most place their estimates at 2-3 million units this weekend, though according to Bloomberg, analyst Carl Howe at the Yankee Group in Boston puts estimated sales at nearly 4 million.

The popularity of the iPhone 4S - which was initially viewed as a disappointment when it was announced instead of a new iPhone 5 - is spurring sales to astronomical new levels. But what is it about the 4S that is causing such a buying frenzy among customers?

Siri

Say what you want about how money can't buy you love; we're convinced that with a couple of upgrades, Siri will be able to pick up on the fact that you're sick and have chicken soup and a compress sent to you as you languish in bed. You actually might just find it whipping up the soup in the kitchen. Whether you're a believer or no, Siri does appear to be a significant factor in driving sales. Speaking to CNN, customers waiting in lines in Atlanta praised the voice-controlled personal assistant. I love Siri, said 33-year-old real estate agent Becky Waddell. We played with it in the store. I know for sure it will make me a safer driver.

iOS 5

The release of iOS 5 Tuesday was met with an overwhelming response from those looking to download Apple's latest offering. Old apps and features sporting sexy new improvements such as the editing tools in the Photos app and Reader in Safari are attractive, sure, but it's the new stuff, like the data-based messaging service iMessage, Reminders, and Notifications Center, that are taking the iPhone 4S to a new level, sales-wise. iOS 5 is compatible with iPhone 3GS and 4, iPod touch 3rd and 4th generations, and iPad and iPad2, the increased processing power of the 4S will optimize user experience of the new operating system.

iCloud

iCloud allows you to store up to 5G of non-purchased content - mail, documents, settings, etc. - in the cloud, with purchased content such as music and TV shows not counting against your storage allowance. Additionally, it syncs on all of your iOS 5-installed devices so you're not required to manage it. Free with iOS 5, iCloud takes what other desktop cloud storage products offer and integrates it where you need it most: across devices and platforms and into your on-the-go routine.

Most powerful camera

Almost - almost - without comment, the iPhone has been stealthily replacing the pocket point-and-shoot. Call it a function of Occam's razor, but as the smartphone camera has gotten better, traditional point-and-shoot cameras have failed to outpace it and users have come to rely more and more on their phones for regular day-to-day photography. The newest iPhone camera is 8 megapixels and shoots 1080 HD video, putting it at or above the standard of many of the most popular point-and-shoots on the market. All that and a bag of chips? Yes, please.

Steve Jobs, In Memoriam...Sort of

Do we think that hordes of sobbing and inconsolable Apple fans flocked to stores to assuage their grief around the passing of Steve Jobs by purchasing a new phone? No.

What we do think is that the uncertainty about the future of Apple has led to many customers' to appreciate the quality of those products designed under the tech guru. In an interview with CNN, Atlanta resident Dwight Hill told reporters that I wanted it anyway, but (Jobs' death) made me sort of want it more because this is the last one I know he worked on... I just hope the company keeps going in the same direction.

Will you buy an iPhone 4S this weekend? What features have you hooked on the Jesus Phone?