JSON vs XML
Dave Johnson has an interesting post about the preferred data transport format for AJAX: is it XML or JSON? He prefers XML. So do I. Dave emphasizes the importance of XML on the client: he uses a datagrid to illustrate this. Personally I like the clean architecture when you just load XML to the client and transform it to whatever you like using XSLT. The XML family of standards seems to be a very good fit with the browser world, and - according to Dave's article - the performance is also pretty good.