Besides nice new widgets such as the slider and statusbar, and big performance improvements, the Ext JS library is now supporting the PUT and DELETE http verbs (besides GET and POST) when using their Ext.form.Action class for Ajax Requests. But is that helping us Rails developers? Not really, since most browsers haven't first-class support for PUT and DELETE (yet). Rails uses a work-around for this problem. If you, for example, create a form tag with the PUT method, it creates an hidden form field with name _method and the http verb as value. Therefore you actually have to add this hidden form field in your Ext form manually and continue using POST as method.
Here is their blog post with all infos about this release and other news (such as a new ext js website with more examples!)
Btw, they also show a preview of Ext JS 3.0, which includes a performance-optimized datagrid view. I recently addressed/solved the performance issues in my PrinterGridPanel class included in my PrinterFriendly extension, which is meant for printing and has therefore less view-features.