The most notable change has been removing dependency on HAL, switching to UDev/UPower/UDisks backend. That helps me with being able to eject USB disks/DVDs from Dolphin/Devices Applet in Fedora 14 (the newly attached devices are mounted by udev and I had to use Nautilus to safely remove them, in pre 4.6 era).
But, that is not all. Couple of very nice things surprised me.
One, very nicely organized device hierarchy in Kinfocenter:
Two, BlueDevil – deprecating kbluetooth. (You have to enable kde-unstable repository to install bluedevil).
Three, and this being my favourite, the highlight of 4.6 – the awesomeness of the panel auto-hiding. I always auto-hide my panel, and hope that it would spring up when a window needs my attention.
Well, it never did. So far. 4.6 brings me great joy – now when a window (a chat window in which someone sent a new message) needs attention, the panel auto-rises! Big thanks to Aaron for fixing it for good. The screenshot below shows panel raises itself when one of my friends ping me.