Apple generally releases an update to their mobile operating system (iOS) whenever they announce a new iPhone; the latest update is a big departure from previous updates.
The current update (iOS7) allows those with an older iPhone (4 or newer), iPad (2 or newer including iPad Mini) and iPod Touch (5th generation) to look and function like the new iPhone 5S and 5C.
Unlike past updates, iOS 7 is more than just a feature upgrade (and there are a bunch of them); it's a complete redesign.
Apple seems to be developing for devices with larger screens as they have incorporated lots of new swipe gestures that have long been used in the Android camp.
The original iOS design seemed to be based on being able to easily reach and tap any part of the screen with one hand, but with the introduction of the iPhone 5's longer screen some users with smaller hands found that was no longer the case.
In general, the safest way to play any major update for any device or operating system (from any company) is to let a few million others take it through its paces to uncover the inevitable issues that accompany any major update (remember the first generation of Siri and Apple Maps?).
If you examine the history of iOS releases, you will see a pattern of minor updates shortly after a major update.
When Apple released iOS 6 in late September of 2012 it quickly followed it up on November 1st with iOS 6.0.1 which mainly contained bug fixes.
The same held true with iOS 5 as 5.0.1 was released less than a month later because of some major battery issues.
Those that waited until the first bug fixes were released avoided the irritation of the unknown issues, with battery draining issues seemingly a common theme.
Anytime an update from any company changes the number before the decimal (6 to 7) it signifies a major update. If the numbers after the decimal change, it's typically a minor update or bug fix so it tends to be a more stable version.
The bigger issue with iOS 7 is that it substantially changes how things work, so if you aren't comfortable with change, you should hold off until you see how it works on someone else's device.
Another option if you have both an iPad and an iPhone is to only update one of the devices (preferably the one you use the least) to get familiar with the changes at your own pace.
Going back to iOS 6 if you don't like iOS 7 may be possible in some cases, but it's not a simple matter of flipping a switch, so don't count on that as an option.
If you are one of the millions that like to break the control Apple has over your device via jailbreaking, you will definitely want to hold off until the usual battle between Apple and the jailbreaking community settles down.
We're already hearing the usual complaints about battery life, security bugs and default privacy settings that need to be addressed, so if you wait a few weeks you'll be much more informed.
By the way, with this many new features, you can expect shortened battery life until you figure out which of the automatically activated features you don't need and you turn them off.