It looks like Microsoft and jQuery have made that decision a lot easier, with this announcement from Scott Guthrie:
We will also distribute intellisense-annotated versions that provide great Visual Studio intellisense and help-integration at design-time.
There's more info in Scott's post, but it looks like set to make ASP.NET AJAX even more compelling. Looks like it's time to dive deeper into jQuery!
Link: Scott Guthrie - jQuery and Microsoft
Link: John Resig - jQuery, Microsoft, and Nokia