I've been working on a Silverlight application. I just noticed that the .xap file is now four times as big as it was, what could have caused that?
Here's some other info:
Screenshot of build directories before and after:
(source: deviantsart.com)
Since .xap is just a zip file, rename the .xap file to .zip and open it up and take a look at the files contained. Perhaps you added a large resource inadvertently?