Still 5.0.1, but apparently solves SIM and "No Service" issues that some 4S users have...with an extra Easter egg. I found the story at:
http://www.theverge.com/2011/12/15/2638974/apple-releases-new-build-of-ios-5-0-1-for-iphone-4s
http://www.theverge.com/2011/12/15/2638974/apple-releases-new-build-of-ios-5-0-1-for-iphone-4s
Well-known iOS hacker MuscleNerd recently tweeted an unusual observation about the update: it's the first official 4S firmware with an accessible encryption key for the main file system, meaning you can browse the file system from a PC unimpeded. Lots of folks are pointing out that this means users will be able to get at Siri's files without committing piracy, and that could lead to a field day for Siri hacks. There's no official word from Apple at this point on exactly what's changed.