At least from my point of view, the perceived value of the iPhone increases with each additional device and service of Apple you use. I recently had the opportunity to test a Samsung: While the device itself was great, I didn't even try to get my music or photos synced. I'm so used of Apple flawless integration with each other. That's the challenge.
I use it sometimes when I'm cycling to play certain song, playlist or album, or to get the current time. If it would understand me, it would be even useful.
I'm blown away by the speed. Can you share a few on the architecture behind to archive this? Edit: I just saw on your blog that you already working on a blog post. I'm looking forward :)
I usually start and finish my day exercising. However, motivation comes from recording each workout to measure my progress and adjust training accordingly. It's hacking your body and any kind of hacking is fun :-)
Most applications don't use any sensors at all, yet you have to deal with the situation if you plan to use them. And there is a big difference in designing an application for devices having only a touchscreen keyboard and devices having a physical keyboard.
Software is one side of the coin. The other side is hardware and developers are dealing with different screen sizes, different sensors, different keyboards and so on. Compared to Apple's iPhone, you have to spend a lot of time making your app work on every device.