Jeff King of the webdevtools team has an excellent blog post on "JScript IntelliSense in Visual Studio "Orcas"". He briefly covers:
I haven't had the time to look at all these features but the weekend is not over yet! Get the March CTP "Orcas" bits and have a look yourself! And for those of you looking for more AJAX goodness: a new release of the AJAX Control Toolkit is available for download.