Apple is set to launch iOS 5 today and you can expect the update to pop up in iTunes any time now. The update, arguably the most significant one in iOS’s history, includes a new notification system, iMessage, Newsstand, Reminders, Twitter integration and freedom from the computer, among 200+ features in all.

But what Apple giveth, Apple also taketh away. Users of the original iPad will find that iOS 5 takes away the systemwide Multi-touch gestures that they have grown so used to in the past few months.

For those not in the know, Apple introduced a “developers only” feature in iOS earlier this year that allowed iPad users of all stripes to hook their tablets up to Xcode on a Mac and enable systemwide four- and five-finger Multi-touch gestures on them.

You can swipe up with four or five fingers to bring up the multitasking panel and similar swipes to the left and right allow you to switch between running apps. A pinching gesture using those same fingers can bring you to the Home screen from whichever app you may be in. As an original iPad user, I can attest to the fact that these gestures increased the usability of my iPad and the swiftness of my interactions with it several fold.

In the few months that I have been using these features, I have grown to love them immensely. The only time I ever use the Home button on my iPad now is to turn on the display when the device is locked. As with Apple’s trackpads and Mac OS X Lion, which prevent you from being able to go back to other trackpads and operating systems once you have gotten used to them, any iPad without these gestures seems much less usable.

But that’s just what you are going to have to contend with if you update your iPad to iOS 5 when it is launched later today. While Apple has fully implemented the feature for the iPad 2, removing the need for users to enable it through Xcode, it has removed it from the original iPad. Given how well it works, we’re as surprised by this move as we were about the announcement that Siri would not be supporting the iPhone 4.

If you have never used the Multi-touch gestures I have described above on your iPad and don’t care to start now, or if you have but think you can live without them, by all means, upgrade to iOS 5. If you are using an iPad 2, you should definitely update to iOS 5. Apple has packed it to the seams with some amazing features and the mad rush to update to it that we will be seeing later today will be justified.

However, if you have gotten used to the Multi-touch gestures on your first-generation iPad and think you can live without the new notifications and all the other fancy features coming in the impending update, perhaps you should stick with iOS 4.3.