I have been away from .NET development for a few months since I started to develop games with the Unity3D engine. However I try to keep up to date by reading articles and implementing small prototypes once in a while.
PDC 2010 started today and surfing the web for comments, articles and online webcasts I found this article with great development tips for the Windows Phone 7. The tips are focused on performance for Silverlight apps running on the phone and this is one of the most complete and detailed articles I have come across.
Make sure to check it out and use it. I love the first part describing how being flexible regarding design patters is a must for performance optimization. We (software architects) tend to over engineer applications just to adder to design patterns and sometimes we sacrifice performance just to keep the pattern architecture, when in reality performance will be much more appreciated by your users.