I'm doing something in Silverlight, but it's just to have a rich version for 1.0. We'll immediately hedge it on release with a JS/CSS/Canvas version. I agree with Scott that it has performance issues, but nothing that's causing a real problem. Also we're storing the data on S3 and eventually the main logic engine on EC2, so the idea is that it's only for a rich, but very dumb, UI. I'm still, at this stage, happy with the decision to use it -- if that helps you at all.