CRM 2011 Code - Export Solution (.NET)

          //Export a solution
            String outputDir = @"C:\solutions\";

            ExportSolutionRequest exportSolutionRequest = new ExportSolutionRequest();
            exportSolutionRequest.Managed = false;

            //Specify the unique name of your solution
            exportSolutionRequest.SolutionName = "TestSolution";

            ExportSolutionResponse exportSolutionResponse = (ExportSolutionResponse)crmServiceDev.Execute(exportSolutionRequest);

            byte[] exportXml = exportSolutionResponse.ExportSolutionFile;
            string filename = "TestSolution" + ".zip";
            File.WriteAllBytes(outputDir + filename, exportXml);

            Console.WriteLine("Solution exported to {0}.", outputDir + filename);