The update includes a small handful of fixes. Among them: Taking HDR photos from the Lock Screen shortcut should now work more reliably. Safari bookmark and Reading list syncing is also improved.
Bugs that prevented the the third-generation iPad from successfully switching between 2G and 3G networks are also addressed. Other bugs afflicting AirPlay video playback are corrected, too.
And if you’ve ever seen an “Unable to purchase” alert after successfully purchasing something on iOS, good news: The 5.1.1 update also resolves that issue.
You can install the update directly from your iOS device, if you’re running iOS 5 or later: Launch Settings, tap General, and then tap Software Update. As a delta update, the iOS 5.1.1 upgrade is a much smaller file than iOS updates before iOS 5 generally were; on my iPhone 4S, the update weighed in at less than 60MB.