Apple users the world over got their first chance to use iOS 6 on iPad, iPod, and iPhone on Sept. 19. The verdict? Stunning features, surprising flaws. Apple might be known for sleek presentation and innovation, but as if with any major upgrade, even for all the good, there have been plenty of hiccups along the way.

Watch out for these three issues when you download iOS 6:

1) Downloading the update

The troubles started with the process of downloading the massive update itself, which clocked in at a hefty 2.5 GB. iOS 6 is an "over the air" upgrade, meaning no connection to iTunes is required. It also meant that millions of early adopters were all trying to grab the file at the same time when it first appeared in Software Update Wednesday morning.

Apple servers seemed to hold up pretty well under the pressure, although users saw wildly different download times depending on their connection, location and time of day -- from a few minutes all the way up to 5 hours.

Many found a greater problem was in store when the update installed itself, and froze with an apparently empty progress bar. If they were patient, however, the bar would suddenly show a lot of progress very fast -- as much as an hour later.

2) Wi-Fi

The new OS has had its share of troubles, most notably a Wi-Fi login bug that Apple quickly and mysteriously resolved.

Attempting to log into Wifi network their phones and tablets had previously recognized and stored passwords for, users were assaulted with a Log In page that directed them to a non-working URL at Apple.com.

When confronted with the bug, the company acknowledged that it had existed, but shouldn't be a problem anymore. Sure enough, whatever switch was flipped on the back end worked, and the Wifi bug vanished.

3) Music

Other users saw ongoing problems with accessing music on their iPhones. Some users reported that their Music libraries had suddenly vanished. Playlist, Artist and Album names all remained, but the tracks themselves were unavailable.

A spinning wheel in the upper left corner of the device's screen indicated that the Music app was trying to access something, but the songs remained stubbornly invisible, even to Siri.

What we love about iOS 6

Major upgrade for Siri:

You can now get sports game updates, make restaurant reservations on OpenTable, watch movie trailers and more on Rotten Tomatoes, launch apps, and even tweet by voice. Siri is now also available for the iPad.

App Store:

According to a report today, the App store is getting a one touch download for free apps. Fantastic news for everyone sick of the three clicks it currently takes.

Facebook Integration:

Facebook will integrate with iOS 6 in a similar way Twitter currently integrates with iOS 5.

New Phone App Features:

You can now set reminders to call people back, send messages instead of calling, apply a "DO NOT DISTURB" feature that does not alert you with notifications.

iCloud Tabs:

iCloud Tabs will integrate Safari across all  iCloud-connected devices, allowing users to go from device to device with the same internet browsing tabs remaining open on each.

Mail VIPs:

iOS 6 Mail VIPs will enable to users to mark certain contacts as important, and in turn, all their messages will be starred.

FaceTime over 3G:

Once reserved for Wi-Fi only, you can now FaceTime over your cellular network.

Photo Stream:

Photo Stream will allow you to easily share photos in real-time with your friends. Sounds familiar to us ... cough Samsung Galaxy S 3 cough.

Guided Access:

Guided Access allows you to lock an app when it's in use so that other controls won't be accessible.

Passbook Potential:

We've already discussed the great potential of Apple's new Passbook app, and there's a lot to get excited about here. The app is one of only a few technologies poised to bring us the next big tech innovation crown: making your phone a digital wallet.

Passbook is an app that will put all your digital coupons, tickets and loyalty cards in one place, and potentially, be a way one day to use the iPhone as a digital wallet. There has been much talk in the past few years about turning phones into digital wallets -- letting people use their phones to surf the Internet, make calls and pay for lattes and muffins.

"Every opportunity I have to get in front of a client, it's the first thing I talk about," says David Reeves, vice president of the 22squared advertising agency. "This is huge. Apple doesn't do anything halfway. This is a tremendous opportunity to revolutionize the way we use our wallets."

The iPhone 5 is choosing Passbook over NFC, partly because many analysts, like Shaw Wu, an analyst at Sterne Agee, argue the technology just isn't there yet, and that the chip hogs too much battery power.

But Wu does expect Passbook to pave the way for mobile payments eventually. Apple just has to get a critical mass of consumers using it. At that point, Apple will be able to persuade retailers to modernize their payment equipment to work with the iPhone.

Visa, MasterCard, Starbucks, Google, Square, PayPal, Intuit and others have been working feverishly to make mobile payments a way of life, but the practice has yet catch on in the mainstream, because businesses are waiting for it to become more widespread.

"With Passbook, you can scan your iPhone or iPod Touch to check in for a flight, get into a movie and redeem a coupon," Apple says on its website. "You can also see when your coupons expire, where your concert seats are, and the balance left on that all-important coffee bar card."

"Your mobile device will become your wallet. Whether it's in a few months, a year from now or longer, it's going to happen," Daniel Delshad developer of a new app, Loyaldash, says.

According to Wu, the long-range game plan for Apple is to have the smartphone do everything -- start the car, lock it, open the house and garage, turn on the air conditioner and heater -- and, of course, become the vehicle to pay for goods with a swift swipe of the phone.

"(Passbook) is just the beginning," Delshad says.