To me, that is not the worst part. It is the app kill/multi-tasking thing. This actually hit me the other day, for the first time, where I could not use Sense to do what I wanted to do... which was actually quite simple. All I wanted, was to have a PDF open in Adobe Reader, and a text editor open for taking notes. I would get a few seconds delay switching to either, and the text editor would even lose the changes if I had not saved it before multi-tasking away. VERY annoying. And unless I am mistaken, not fixable on Sense. I flashed my CM10 backup back on, and instantly (well, 5 mins to flash) had it working "as expected".
Actual loss of functionality, for no apparent GAIN I am aware of... I hope HTC reverts their multitasking with Jellybean.