The fact that Microsoft think it is acceptable to have enough of a delay inbetween switching apps to warrant designing in a "Resuming . . . . ." dialogue to make you acutely aware of this, instead of masking it with something pretty, is beyond all belief. How iOS deals with this, and has for years, is that it masks any load times or delays with elegant, fluid zooming in/out animations which, whilst not getting you to the app faster, don't come across as half-baked and draw attention AWAY from the mundane, ugly fact that they are drawing your attention towards MORE by telling you they've not solved the problem, and are, instead, content with making you stare at a "Resuming . . . . ." dialogue with NOTHING about it which could ease your annoyance at that app not having loaded faster.
Think of it like this: if you're sitting in a busy restaurant with hungry children and there's a big queue, what's more likely to make you return to that restaurant for another meal:
#1 Free drinks whilst queueing, and nice surroundings (distractions, but they WORK), and colouring books for your children and maybe a TV to watch?
#2 The owner coming back every few minutes and apologising profusely, further drawing your attention to the inconvenience repeatedly?
I love LOVE Windows Phone platform, but since I come from a mixed iOS/Mac user background, the flaws which are never EVER seen on iOS due to this innovative use of animations and beautiful screens to stare at WHILST things load behind the scenes, are shamelessly laid bare and with no attempt to soften this blow by persisting in having "Resuming . . . . ." ... Microsoft may find that they need to re-assess their design model before they are taken MUCH more seriously than at present; the aesthetic of Windows Phone is minimalist and, whilst that does a LOT in it's favour, it serves to offer a HUGE negative in the respect of being forced into a black void with five animated dots 15+ times a day!