The new Dojo 1.6 toolkit has just been released! Check out the what’s new page on the Dojotoolkit site. I think the best thing in this release is the refactoring of all of the dojo and dijit classes to support CommonJS Modules/AsynchronousDefinition (AMD). It also has a bunch of other really nice things like dojo.replaceClass and dojo._getMarginSize for performance gains in Internet Explorer 6 and 7. Those two features will be very important for an optimized runtime and download speeds.
All modules in dojo and dijit have been converted to comply with the CommonJS Modules/AsynchronousDefinition (AMD) proposal. This is a preparatory step on the way to full AMD support in version 1.7 and beyond. Unless you are an early adopter of using dojo with an AMD loader, these changes should be transparent to you. — link