I also own a WP7 running Mango. It's far easier to use than Android and is probably on par with iPhone, though more innovative than a screen of icons. The app store hasn't been a problem yet for me. You'll find all of the 90% apps (as in the ones that 90% of the people use). Where you can have some trouble are apps made for a specific companies services such as bank apps, though I use the mobile site instead.
The wifi does switch off when the phone is locked but only when it's not plugged in. This is purely to save battery. You can turn the 3G off in the settings so that it never uses it, though being a smart phone, you have to have some data service or else the phone company won't hook you up.
Getting pics is done through Zune which is fine, but not as straight forward as a mounted hard drive. There is a trick you can do to mount it as a hard drive, but I haven't tried it but supposedly once it's done, it's easy after that.
I really like my phone (Samsung Focus). In fact, the only reason my wife (who is very non-technical) went from a feature phone to a smart phone was because she saw how easy mine was to use. Android intimidated her. I'm sure she would have been fine with an iPhone as well, I just hate the ecosystem that's thrust on you.