Unfortunately Ext JS 2.1 (and Ext GWT 1.0) have been released under the GPL. This will make Ext more difficult to sell to corporate clients.
Ext JS 2.0.2 is still available for download under a LGPL licence and can be used with the GWT integration found in the GWT-Ext project (not to be confused with Ext GWT). i.e. GWT-Ext 2.0.3 and Ext 2.0.2 are still both LGPL. I wonder if Ext GWT 1.0 (GPL) started life as GWT-Ext 2.0.3 (LGPL)…
I discovered a promise of a tibcogi4gwt project but nothing more :(
Update: more info can be found in a post by the author of GWT-Ext.