My Samsung Galaxy S III downloaded the latest Android OS (Jelly Bean) and firmware by itself. It just prompted me if I wanted to install it already. The installation process went very smoothly except for a minor inconvenience -- it complained that my external SD is damaged. I've suspected before that I might have removed it improperly as a USB device so it did not get ejected properly. I had to reformat it to make it usable again.
The new OS seem zippier (or maybe its just my imagination). For one, I am happy that they re-positioned the Bluetooth icon in the pull-down menu to be accessible on the first screen. With the previous OS version, I had to do an extra swipe to the right just to be able to access it.
There is also a multiple window support now. I'm sure this is handy with a tablet but I don't know how useful it is for a Smartphone with a small screen anyway. Splitting your screen further into multiple windows does not really give you that much real estate left. It is kinda cool to see both Facebook and GMail on a tiled layout within the same screen though.
The "desktop" already support folders similar to iOS. So multiple icons on the same screen can be grouped together into a "folder". Clicking the "folder" will expand it to what's contained inside.