Looks interesting, but no support for IE6 and IE7 can be a deal-breaker for many users, especially when there's 960gs (http://960.gs) which supports those browsers.
as someone who deals with the front end for a company whose business is a web app, no support for ie6 (with patch files, conditionals, whatever) really is a deal breaker. the sad fact is 15% of our customers still use ie6.
draw your own conclusions, but those customers generate significantly higher revenues per customer than those who use modern/semi-recent browsers.
"Safari 3, Google Chrome, Firefox 3, Opera 9 and Internet Explorer 8 all work correctly with some minor differences."
Seems like cross-browser compatibility (including Firefox 2, IE7, and heck if you're making a framework, IE6) would be at the top of the list of your priorities when creating something like this, though ;-).
extjs, qooxdoo and cappuccino on the Javascript side, GWT and Vaadin for Java, Pyjamas for Python. Especially Java seems to have lots of "component-oriented frameworks".
