After a short discussion in silverlight forums with a guy who have only 19kb line, I checked out compression for XAP files. A XAP is a zipped package of DLL’s and resources. With winrar installed you can open by context menu from Visual Studio Explorer the xap (clientbin). It contains files like
The size of the package in this case is 750 KB. I unzipped the content and compressed it with Winrar again and- surprise- surprise, package size is now 547 KB. A reduction more than 35%. Only rename the zip back to xap.
I will investigate a little bit, how to automate that within the build process.