The debugging experience in Silverlight project using Visual Studio is quite good. However, there are two things that is doesn’t help much with: when data bindings don’t work, and when your XAML doesn’t look like you think it should. Here’s a post about debugging data bindings. The visual part is a little more involved. Yes, yes Expression Blend has a nice visual designer, but it’s fairly common for Blend to show a piece of XAML in one way and for it to actually render in the browser differently (sometime significantly differently). Today I found First Floor Software’s Silverlight Spy. This appears to be a pretty awesome diagnostics tool that allows you to see and alter Silverlight’s Visual Tree at runtime side by side an embedded browser.
You can edit the Visual Studio within Silverlight Spy and see the rendered content change immediately. This is extremely useful. This is to Silverlight apps what Firebug is to web apps.
If this is still useful at the end of the trial period, I’ll be buying a copy of this for myself.