It looks like the last piece of the iPad puzzle may be falling into place. With the launch event for Apple’s latest tablet less than 24 hours away, reports are circulating this afternoon that the gold master version of iOS 5.1 has been undergoing Apple’s thorough QA testing for about three weeks.

Citing a “very solid source,” Chronic Wire says that iOS 5.1 is nearly finished with both Apple’s internal testing and similar testing with carriers and other partners. Apple has not made this version of iOS available to developers yet.

There hasn’t been a lot of attention given to the features of iOS 5.1. Most of the focus has been on the iPad 3 (iPad HD?). That said, we know a little of what to expect. For one thing, Siri will be learning Japanese, according to Siri herself. Facebook integration is at least possible, since references to Facebook were found in earlier betas of iOS 5.1 back in January. Chronic Wire’s report also suggests that iOS 5.1 will be getting an easier method of accessing the camera from the lock screen (a nifty feature introduced in iOS 5 last year), as well as “at least two other new features that have not been publicly leaked.”

It’s likely that iOS 5.1 will release either sometime tomorrow (after the iPad launch event) or sometime later, closer to when the iPad is actually released to the public. In either case, it’s a pretty safe bet that the iPad 3/HD will run iOS 5.1 right out of the box.

What are you hoping for from iOS 5.1? Let us know in the comments.