Tonight, or this morning as the case may be, I was running into an issue with jQuery and the getJSON method. Basically, I was calling the method, with the proper parameters, but nothing was happening. The server method wasn't being called, and JavaScript debugging alerts weren't being fired either. After fiddling with the JavaScript for awhile, I decided to check out the JavaScript debugging feature which was added to Visual Studio 2008.
Since I'd never used it before, I did the most logical thing I could think of, I searched. It turns out that JavaScript debugging is very easy to setup.
First, go into your browser and enable script debugging. For Internet Explorer 7, go to Tools | Options | Advanced, and uncheck 'Disable script debugging (Internet Explorer)' and 'Disable script debugging (Other)'. For Firefox, JavaScript debugging appears to be enabled by default.
Next, in Visual Studio, type Ctrl+Alt+P to open the 'Attach to Process...' dialog, and select either firefox.exe or iexplore.exe depending on which browser you are using.
Finally, set breakpoints in your JavaScript code, and perform the action in the browser to get to the breakpoints. After that, you can use the standard Step Into and Step Over to navigate through your JavaScript. Visual Studio also provides debugger tooltips to explore your JavaScript objects, which is what ultimately led me to the response of the XmlHttpRequest object, and the realization that I had mis-named a server method parameter.
With the popularity of jQuery, and other JavaScript libraries, I foresee this feature being widely used among web developers.