It does seem random, doesn't it. I always seem to get updated very early, which surprises me as I'm not on a phone contract but SIM only, though I did buy the phone from O2 and it is O2 branded. Anyway, survived it. Always a worrying time, when I hear how other people's phones get bricked.
Haven't had much of a play yet but but I can tell you this, although it has been reported previously, I think. The new "storage check" only appears (as the last item in Settings) if you go into then out of "phone storage" in Settings. Weird. A feature, or a bug before we've started. Incidentally, just installing the update freed 250MB.