Loving it on my N4, no need for full wipe, just installed over the 3.15 nightly and working fine. Takes a bit of tweaking to get it up, and only seems to work on Phone UI, not any of the tablet ones. No way to enable it from PIE, have to turn PIE off, enable it, and then switch back to PIE. Would love a way to enable it from the notification pop up whole using PIE, and to have it work in the tablet UI's. Also would love for the dismiss to the X at the top of the screen to not turn it off entirely, just make it dissappear from screen until another notification brings it up.
Things I'd love to see: an opt-in or opt-out for apps/notifications. I don't necessarily want every notification going to Halo. Also a way to move from one notification Halo to another, hace multiple notification Halos (have seen some mockups for it and know you're working on it!). But even in its current state it's awesome.