WordPress 3.5 was released on December 11, 2012. I just did my first install.
It looks like another release chocked full of useless bells and whistles. There is a new theme called TwentyTwelve 1.1. It is a much more plain Jane theme than TwentyTen or TwentyEleven. The theme uses rems, rather than pixels as the unit of measure. It looks like another grandiose experiment.
I primarily use TwentyTen as the basis for custom sites, which I found to be a rock solid theme.
In my opinion, TwentyEleven was so loaded with useless bells and whistles that it was the equivalent of ten pounds of crap in a five-pound sack. It also runs slower than TwentyTen.
After using CSS for the past 10+ years, I did not even know that there is a rem unit of measure. I will have to build a site with TwentyTwelve before I pass judgement on this one. I see that Simple Pie has been added to the wp-includes directory, but I do not know how it is being utilized.
At this point, I do not see any benefits with the new release. Please toss your two cents worth in if you see something worthwhile.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin