Apple's new line of 11-inch and 13-inch MacBook Air notebooks, which went on sale on Wednesday with the new Mac OS X Lion pre-installed, will pose a threat to PC sales, according to analysts.

PCWorld predicts that MacBook Air will be the go-to device for executives and professionals. And we agree because the updated MacBook Air features the return of a backlit keyboard, a minimum of 128 GB solid state drives (SSD) and 4 GB of RAM, which the Apple fans have been waiting for.

Nearly 400,000 units of the new 11.6-inch and 13.3-inch MacBook Air, equipped with powerful graphic chips, Thunderbolt data port and Intel's ultra-low voltage Sandy Bridge processors are set to be produced this month and with OS X Lion pre-installed (which AppleInsider calls the latest and greatest Mac OS ever launched), they could pose a serious threat to the PC industry.

While the Thunderbolt port allows users to connect various devices like a display or external drives, and helps move data 20 times faster than USB or 12 times faster than FireWire 800, the updated processor and use of SSD lets the new line of MacBook Air run 2.5x faster than previous models.

However, what actually makes the thin and light MacBook Air stand out from the crowd is the OS X Lion it comes pre-installed with.

Os X Lion replaces the outdated Mac OS X 10.6 (Snow Leopard) and it represents a quantum leap in terms of OS advancement as it not only features enhanced security features (Mac users who became the victims of MacDefender malware will be happy to hear this) but also it boasts of other nifty features such as AirDrop, which allows for quick and easy wireless file transfers to those around you (the way Bluetooth works). AirDrop will allow peer-to-peer Wi-Fi between participating users without a needed wireless network. No infrastructure is required. It's as simple as 'drag and drop.'

But what makes Lion unique is it centralizes all your content in one place using Expose and the new feature of Mission Control. With a swipe, the computer desktop will zoom out to display opened windows grouped together within an app, thumbnails of the full screen apps and the Dashboard. With just a tap, it will allow you to instantly navigate anywhere.

OS X Lion also integrate Multi-Touch gestures that will let users interact with content on the screen ith a swipe, tap or pinch.

Also, OS X Lion features a Launchpad, similar to the applications folder, but it will be in full-screen view, displaying the apps.

Other features of OS X Lion include:

Resume - It brings the system back as they were left after the computer is restarted

Auto Save - It regularly saves work so you don't have to

Versions - It records history of documents as you create them, providing an easier way to browse, copy, and paste

Time Machine - It keeps a spare copy of the files you create, modify, or delete right on the Mac. It is helpful when you accidentally deleted a file as you can now can recover it from a local copy

FaceTime - IT allows you to make video calls to any friends who are using Intel-based Mac computers, iPad 2, iPhone 4, or the latest iPod Touch. You can smartly switch between a call and other apps while still in full-screen view. You can hear FaceTime ring even if it isn’t running, when someone tried to reach you, and

iCloud - With OS X Lion, you have access to iCloud, Apple's ambitious cloud-based music, video, photo and data automatic backup and push out service. It represents a major new direction for Apple, which sees it as a way of tying together its various desktop and mobile platforms, as well as providing an additional method for delivering media to users. Unlike Google's or Amazon's cloud-based service, which requires users to upload their songs or data, Apple iCloud will be able to automatically scan a user's library and make mirror copies available instantly.

According to J.P. Morgan analyst Mark Moskowitz, Apple has timed the launch of the new MacBook Air right because it could turn into a $3 billion business-a-year, especially with iCloud equipped. In April, Moskowitz estimated the MacBook Air to be a $2.2 billion business.

Sales of ultra-thin MacBook Air have surged even as sales of fatter notebooks and desktop computers stagnated - MacBook Air sales rose 2.9 percent over the prior quarter, even as the broader PC market slipped by 10.1 percent and overall Mac unit sales fell 10.5 percent.

Moskowitz estimates Apple will sell roughly 700,000 of the notebooks each quarter - up from just 432,000 units in the first quarter of 2011.

The MacBook Air increasingly will be recognized as offering users tablet-like functionality - ultra-portability, thinness, and instant-on - while offering an integrated keyboard and a full computing applications suite to complete professional work-related tasks, Moscowitz wrote to his clients.

On top of that, with users storing more of their data on cloud-based services, with OS X Lion offering Apple's iCloud services, the new notebook could become a breakout product for Apple.

Agrees Ben Reitzes, an analyst at Barclays Capital. While product refreshes are generally a standard practice (faster, better, same cost), we believe the MacBook Airs could eventually replace the traditional white MacBook that remains in the line currently, Reitzes said.

Reitzes said Apple's last MacBook Air refresh was in October 2010 where the company went to an all new design.

The analyst noted that MacBook Airs do not use HDDs and he expects many PC players will attempt to copy Apple's form factor by 2012. He believes MacBook Air sales will accelerate significantly into the holidays and become much more prevalent as a percentage of Apple's sales with each upgrade.

Reitzes also believes the new MacBook Airs will help support his estimates for Mac sales growth of 24 percent year-over-year for the September quarter and 23 percent year-over-year for the December quarter.