I have been a fan of the multi-window thing since ages when I used to use my S2, Note or i9305 as my secondary phones but once my N9 gave up many moons ago, I just dont use multi-window much.

It become so rare that I switched to MIUI and never missed multi-window. One thing I do like about Android is the pop-up windows for video players that can be dragged around so if I am for example playing sudoku I can put it at the bottom or top and view my music videos. Multi-tasking is also improved with things like LMT Pie Controls, Switchr etc so Android has some cool things that try to make up for its crippled multi-tasking methods.

However, the crap I have to put up with to do basic things like rsyncing, SSHing over USB (w/o using adb) etc make me long for the day Sailfish is ported over to my i9305 or Nex4. Hopefully by then Sailfish is more mature as in its current infancy it lags behind Android for my current usage patterns (i.e. proper Cal/CardDAV etc).