Along with the shiny new iPad hardware, Apple has released the newest version of its mobile operating system, iOS 5.1, which is compatible with the iPhone 3GS, iPhone 4, iPod touch 3rd Generation, iPod touch 4th gen, iPad, iPad 2, and “new iPad.” I got prompted to update the software last night. If you haven’t seen this yet, go into Settings > General > Software Update and get it for yourself (back up your device first). While the only major benefit to 5.1 discussed in the keynote was Siri in Japan, there are a few additional touches in the system that improve the iDevice experience.

So what do you get? First, you can now delete photos from the Photo Stream on any iOS 5.1. device. The deletions will only appear effective on devices running iOS 5.1. Additionally, you will only be able to delete photos uploaded to the photo stream on a 5.1 equipped device, so those older photos will remain for 30 more days. You can clear out the entire Photo Stream on icloud.com.

Next, Apple’s has improved the quick camera access via the home screen – no longer will you have to double tap the home button to bring up the camera button. Now the camera button will appear on the bottom right corner of the home screen: simply slide the camera button up to access the camera and slide it back down when done.

Next, iTunes Match has been improved. You can get Genius Playlists and Mixes now. Settings now includes a “use cellular data” option so that you can shut off streaming when away from wifi. Along with the  iTunes 10.6 update that came this week, users are reporting smoother, less bumpy playback so it appears the new OS fixes some bugs.

The new OS also adds greater granularity to the location notifications – check Settings > Location Services, where the new notifications are described. The notifications will show which apps are using what types of services.

iOS 5.1 comes with improvements to the iPad camera and facial recognition as well. Playback speed and skip back controls are now available in iPad podcast player. And, a curious “4G” indicator is now showing up on iPhone 4S – no, this doesn’t mean that your iPhone is now 4G capable. It appears to now detect when you are in a HSPA+ network. The new iPad will show an LTE indicator when it is actually in an LTE network.

That’s about the size of it. While not earth shattering, certainly better than the old version so its worth updating.