In my work with version 3.1a I ran into problems with collisions in the javascript libraries used that (so far) have prevented me from using certain controls on pages together and caused problems with outside javascript.
I know it's probably late in the game for the version 4 release, but at some point you might consider switching over to the JQuery library as a base. It is a powerful library with lots of plugins for many functions. It will also be incorporated in the next release of Visual Studio. As a matter of fact I allready have a plugin that provides JQuery intellisense in VS 2008.
This would make implementation of javascript in your application much more reliable and extensible.