how to find out which part of the application is dragging the UI responsiveness down?
the profiler integrated in VS shows a graph based on a time-line, but is does not indicate which part of the application is responsible for the low performance.
This is a really broad question but I have found this Channel 9 video by Jeff Wilcox really helped highlight all the low hanging fruit for Windows Phone 7 app optimization. The video is called "Analyzing and Improving Windows Phone Application Performance" and can be found here: http://channel9.msdn.com/events/MIX/MIX11/DVC01
Good luck!