I've had both iPhone and WP7.5. I like the windows phone better. The only thing that is really annoying is that the facebook integration doesn't filter out all the game statuses, etc. This is due to an integration issue since it is an external app and I beleive the claim is that they cannot do that with an external app. The graphics are responsive, the live tiles are really nice, I like having them. The UI design with the keyboard (on the HTC Titan) is really nice, I like the keyboard staying on the bottom and the suggestion bar as well. I like that the browser address bar is on the bottom and always visible. This lets you interact with it without putting your hands in the viewing area. I think they should go further with the theme and let you colorize the main tiles to different colors instead of restricting you to one color. There are a few minor things that can can be corrected, such as if they have a .com button on the keyboard and the last character you typed was a period, it would be left with ..com. This can be easily addressed. Overall, I do like it better than the IPhone, especially having a device with a larger screen. I can type faster with the windows phone and make corrections easier as well. The suggestions bar works much better than the suggestions on the IPhone.

I'll bite, because I have an application that does change the toolbar icons based on context. This might not match their case, but what happens when you have lots of actions based on context. You have various different element types, and displaying all the icons (with most of them disabled) could take up more space than we have allocated on the taskbar. But if you change the icons based on context, the user can quickly see what actions are available, instead of having a sea of disabled icons that they have to mouse through. And keeping their relative actions close to the working area could be more ergonomic. I'm not sure if this matches the dynamics of the Solution Explorer. It may not have enough operations that warrant the change. But if it does, its one way to make better use of the available space.