As detailed in the post jQuery: Blog: » jQuery 1.0.4 there are quite a few bug fixes as well as some enhancements to its AJAX functionality. While the new additions are useful, the fact it is a point/minor release (i.e. from 1.0.3 to 1.0.4 rather than to 1.1) can be of an issue as generally minor releases are for bug fixes only not API changes. Although, to be fair, it looks like nothing was removed from the API and if you tried to use the new features on a page using the old version, they simply would not work. Like in previous releases, a lot of the fixes have been provided by Jörn Zaefferer.