jQuery may/has become the de facto standard Javascript framework if you believe various sources on the web. And I do. Using jQuery in Seaside is a pleasure. (I've never worked with Scriptaculous though.)
In February a new version of the base framework was released and earlier this month a new version of the UI plugin. Both include many fixes and enhancements and claim major optimisations. The UI plugin has a new CSS framework as well.
Lukas Renggli is very fast to update the Seaside bindings for jQuery (UI), making it easy for me to release an adapted version for VA Smalltalk 8.0 beta1 soon after.
You may have experienced a problem when trying to download jQuery from VAStGoodies.com, because both the VAStGoodies server and the client couldn't handle the $/ in the jQuery Configuration Map names. That has been fixed today. Update your client and check it out.
We interviewed John Resig on FLOSS Weekly a few weeks back (http://twit.tv/floss55), and I must say that after looking at jQuery, I'm very impressed at how much is done with so little intrusion. I look forward to Seaside's support of jQuery in addition to prototype/scriptaculous support.
The "JQuery-WidgetBox" package in http://www.squeaksource.com/SeasideExamples.html provides a wrapper for the "splitter control" and can be used as an example how to wrap other JQuery extensions you will find on the web