As Apple announced last week, iOS 4.1 is now available for download and installation via iTunes. I recommend that you install it, assuming you have an iPhone or iPod touch that can run it, meaning any iPhone or iPod touch other than the first generation of either model. iPad users must wait for iOS 4.2, scheduled for release in November 2010, before they get iOS 4 features.
Lots of people have already updated to iOS 4.1 without a hitch, and the new features and fixes make it a worthwhile update. Some changes, such as better performance for the iPhone 3G, more complete Bluetooth support, and HDR photos on the iPhone 4, make these devices more useful; other changes, such as iTunes Store TV rentals and the new Game Center, will make them more entertaining to many users.
If you have an iPhone 4, you'll find a few iOS 4.1 changes that aren't available on the other devices:
In the Camera app, HDR (high dynamic range) photo support should help you take a better photo with no extra effort, but at the expense of a few more seconds of post-shutter-click processing. Look for an HDR On/Off button on the screen as you take a photo.
If you record HD video, you can now upload it via Wi-Fi to YouTube and MobileMe.
While you hold your phone up to your ear during a call, the proximity sensor should be smarter about realizing that any button taps are being accidentally made by your head, not by your finger. This should prevent some calls from dropping.
I've read a few reports that suggest that this fix isn't working for everyone. If it's not working for you, try holding the iPhone normally against your ear and cheek during a call - you may have trained yourself to hold it away from your face because of previous dropped calls. I've also read the suggestion that you may solve residual proximity sensor problems by resetting the iPhone's settings in Settings > General > Reset. Tap Reset All Settings. Of course, you'll now have to recreate various user-generated settings, so don't do this unless your desire for a possible fix outweighs the trouble of losing your settings. You may also want to wait a few days and see if more information becomes available.
If you have any iOS 4-capable device besides the iPhone 3G, the new Game Center app will appear on your home screen, giving you access to multi-player games.
And, iOS 4 makes these changes, no matter which iOS 4-capable device you install it on:
In the iTunes app, you can now rent TV shows.
Playback controls on AVRCP Bluetooth accessories should all now function properly. For example, buttons on a Bluetooth headset for advancing music to the next or previous track should now work. AVRCP, in case you're wondering, stands for Audio/Visual Remote Control Profile.
If you have the Nike+iPod device, look for changes in the Nike+ app. According to the impressively detailed about iOS 4.1, the Nike+ app now can sync with its Web site and has fancier options for interacting with the site.
Parental controls in the Settings app now let you disable FaceTime "phone" calls, as well as the multi-player option in Game Center.
You can read more about the new features and fixes in "" (1 September 2010).
An important additional fix listed in Apple's release notes is better performance for the iPhone 3G. Following up on my article "" (27 August 2010), I installed the update on my iPhone 3G. I can't tell if the iPhone 3G is exactly as fast with iOS 4.1 as it was with iOS 3.1.3, but it seems about the same. Many reports on the Web confirm my impression. If you'd like to see for yourself, watch the  video at Lifehacker. Thumbs up to Apple for not leaving the iPhone 3G abandoned on the highway of progress, though it would have been better if iPhone 3G owners hadn't had to suffer months of poor performance and poor communication about the problem.
Although several people have reported that iOS 4.1 has solved performance problems on the second-generation iPod touch, Apple said nothing about it in the release notes for iOS 4.1.
Further, a new feature of iOS 4 overall is that notes from the Notes app can sync with MobileMe. In iOS 4.1 Apple inexplicably removed this feature from the iPhone 3G and the second-generation iPod touch. Apple mentions this removal briefly in a that was modified last week. Better release notes would have saved time and trouble for those who unexpectedly lost the capability to sync their notes wirelessly.
(By the way, several readers have commented that one tip or another in the article about speeding up an iPhone 3G improved the speed of an iPhone 3G running iOS 3.1.3. The article is likely worth a read if your iPhone - whatever model - is running slowly.)
Installing iOS 4.1 will take some time, so don't start the update right before you want to leave the house. It took about 30 minutes to download and install iOS 4.1 on my iPhone 3G and about 20 minutes on my iPhone 3GS. In both cases, I was already running iOS 4.0.2. If you're still running iOS 3.1.3, expect the update to take as long as a few hours, especially if you have a lot of content on your device.