jQuery 1.4 was released on Thursday January 14.

New Features and updates include

• Performance Overhaul of Popular Methods
• Easy Setter Functions
• Ajax
• Nested param serialization
• JSON and script types auto-detected by content-type
• Etag support has been added
• Strict JSON parsing, using native JSON.parse
• Serialize HTML5 elements
• Context for Ajax Request
• Success callback receives XHR object as third argument
• Explicitly set a content-type
• Explicitly specify a JSONP callback name 
• Avoid pre-flighting cross-domain XHR
• jQuery.ajax() is now using onreadystatechange instead of a timer
• Attributes
• CSS
• performance improvement
  
• Data
• .data() returns Object and .data(Object) sets the object
• Data cache is no longer created if it isn’t needed
  
• Effects
• Per-property Easing
• Events
• New Method: jQuery.proxy()
• Event Multi-binding
• New events: `focusin` and `focusout`
• All Events Can Be Live Events
  

Need to watch for this important change between 1.3.2 and 1.4
jQuery() (with no arguments) no longer converts to jQuery(document).

Loads more at jQuery 1.4 and we will be updating our ASP.Net JQuery Select transfer lists for jQuery1.4 in the coming days