A couple of weeks ago I followed a two day Windows Phone 7 course (a little thank you to Microsoft for making this course free for Microsoft Partners is in place here). During the course, there were some small issues mentioned you need to take into account when developing for a Windows Phone 7 device that don't seem so obvious. Just to get you started, here's an overview of the most important stuff that's different from regular Silverlight development. I won't go into the gory details, just give you an overview of some stuff that I thought was a bit peculiar or different to what I was used to and some stuff you just need to know, which you don't find easily on the MSDN site.
First of all, when doing Windows Phone 7 development, you can use an emulator to see the result of all your hard coding work. That is, if you don't have the real stuff (which I don't, all donations are welcome!). When working with the emulator, one of the time consuming tasks, is typing in characters (eg. when editing a text box). The emulator gives you an on screen keyboard you can use to type, but this is not very practical when using your mouse! And if you try using your pc's keyboard to type, you'll find your key presses are not accepted.
There is, however a very quick and easy solution to use your pc's keyboard: just press your pause button (you know, the one you hardly ever use) and start to type. Once you're done typing, just press pause again. This will save you loads of time in the emulator.
Next, if you want to use animations in your Silverlight application, there are several ways to start a storyboard. You can do this with an event trigger in your XAML, using code, or by using the visual state manager. When developing for a Windows Phone 7 however, be aware that when using event triggers in XAML, only the Loaded event is available. Because you have this restriction, the better option to start a storyboard animation is by using code, just because it gives you more options.
Another difference is the absence of the NotifyOnException and NotifyOnValidation options you normally have for Silverlight databindings. These are just not there. If you get an error on your databinding, keep in mind, you will not see this in your interface.
If you want to unit test your Windows Phone 7 application you're out of luck. The standard unit test project type of Visual Studio is not compatible with the Windows Phone 7 project type. I am pretty sure however it must be possible to unit test your app using a 'plain old' NUnit class library (which I still think is a better option than the build in unit testing Visual Studio gives you).
One last, very small tip: don't close your emulator each time you change something in your code. It just increases the start-up time when you run your app. It's not a big thing, but it can truly save you a lot of time.
So, there you have it, some small, but still important things to keep in mind when developing for a Windows Phone 7 device. One of my next private projects will be a small 2D and 3D XNA app for the Windows Phone 7 (after teaching OpenGL and XNA a couple of years, I'm just aching to try this). I promise I will make some posts about it. And at this moment at QFrame (my company) we are also working on an (almost finished) Silverlight app for the phone, which uses Azure services and which we will demo at the Belgian TechDays 2011 next week. Be there!