Having installed New Sonar Platinum a few hours ago, all I can say after messing about with it for much longer than I intended (it's 4am here....) things look pretty good so far. Download was straightforward, not as fast as some here are saying but that might be because our ADSL bandwidths are different, or because we're on opposite sides of the Atlantic. Or jsut because. In any case it seemed to pretty much max out the ADSL bandwidth most of the time. Once downloaded the actual install was much faster than the old "click on the installer then go on holiday while it unpacks everything" system.
Third party plugins I've tried (some Waves, Overloud, Jamstix very briefly just to check it loaded) seem to be working as intended. The new control bar is much more like how it should always have been, Rematrix sounds very good. I'd actually have bought the upgrade just to get those two things plus the changes to the sends gui.
Haven't hit it with a big project or really done much besides load up a few stereo tracks I'm giving the finishing/mastering touch to though. Only downside so far is that the CCC thing hasn't picked up that I already had Dim Pro installed and a custom installation can't be customised enough. No option to choose individual plugins, only "suites" of them which means I've had to install quite a few I'm unlikely to ever use just to get the ones I do use.