I've just flashed my N800 with the 0.4, couple findings so far:
- the power button indeed doesn't work, can't shutdown but via removing battery
- once the screen dims, my N800 won't wake up (I think this bug has already been reported in previous releases)
- I can't get the onscreen keyboard to show up - pressing, clicking any other action on a text field doesn't do anything. Could somebody with N800 try that?
- nice new wallpaper

In any case, megakudos to Solca et al for making this happen!!!