Peter Bryzgalov's List: Design - Webdesigh

You can avoid a round trip to the server.

Base64 encode your SVG xml.

Then generate a link to that data. The user can right click on to save it locally.

// This example was created using Protovis & jQuery
// Base64 provided by http://www.webtoolkit.info/
function encode_as_img_and_link(){
 // Add some critical information
 $("svg").attr({ version: '1.1' , xmlns:"http://www.w3.org/2000/svg"});

 var svg = $("#chart-canvas").html();
 var b64 = Base64.encode(svg);

 // Works in recent Webkit(Chrome)
 $("body").append($("<img src='data:image/svg+xml;base64, "+b64+"' alt='file.svg'/>"));

 // Works in Firefox 3.6 and Webit and possibly any browser which supports the data-uri
 $("body").append($("<a href-lang='image/svg+xml' href='data:image/svg+xml;base64, "+b64+"' title='file.svg'>Download</a>"));
}

The img tag works in Webkit, the link works in Webkit & Firefox, and may work in any browser which supports data-uri