Matt Lacey has a nice advice to all WP7 devs who want to make the size of their XAP file as small as possible... with a little help from Telerik!
Source: Matt Lacey's Blog
For an app I've been working on recently (more off than on) I wanted to get the start up time as short as possible. One of the ways I've been doing this has been to remove unnecessary external libraries and to optimise my use of the ones that I do need.
Now, while I'm a big fan of NuGet sometimes I don't want everything in a library. In this instance I created a version of the library I was using specifically restricted to the functionality that the app needs. I did this by getting the source of the library I was using (well actually libraries as there were 2), added the source project to my solution, excluded everything I didn't need from the project and then linked my app to that project rather than the downloaded copy of the compiled library.