I've ranted about this before, but fresh restarts when you click on an app icon is just a bad idea. And now that I have 3 separate family members using wp7.5 devices, it just baffles me how MS can continue to justify it. None of my family members use the card screen for multitasking. Ever. Its just not intuitive. Double clicking the home icon on ios isn't intuitive either, but that doesn't matter because apps don't restart when you click them on ios.
So the end result is that apps take considerably longer to start than for someone using android or ios because you are starting over each time. I understand that it will clash with the UI imperative to have less chrome on screen (since you'll want to have a home icon in each screen), but the tradeoff to an average user is just not worth it. When using 3rd party apps, windows phones are much, much slower than the competition because most users are launching a fresh version of the app each time.