5 Great new Features in jQuery 1.4

1. All Events can now be Live Events (.live) - The magic that is the Live Event no longer has the restrictions the original release put upon it (except in the case of focus and blur, which should be replaced with focusin and focusout).
2. We can now unwrap as well as wrap (unwrap()) - This always felt like a given…and it’s great to finally have it.
3. Clean and easy attributes when creating elements (documentation) - Rather than creating a messy,endless string attributes, we can now combine them all into a clean new form.
4. New nextUntil, prevUntil and parentsUntil methods - Each of these methods traverses the DOM in the desired direction until the passed selector is satisfied…this is a great addition for form validation.
5. New .detach() method allows element removal with deleting data - This is great for complex application state changes in which you’d like to hold on to removed elements for later, rather than recreating them from scratch (the data saved includes information attached via .data() method as well).

For a more intense/in-depth overview of the new features, checkout Day 1 of the 14 Days of jQuery website.