We wrote the apps below which is an all JS front end, and skinnable product for event media, It was written with Dojo which in my opinion is the toolkit that is geared towards large JS web apps, we have built large web apps, in virtually ever toolkit and Dojo is pretty unanimous among the development team as the one that makes building large apps maintainable and rapid to develop, We opt for jQuery for small widget stuff that will just get added to pages and to spruce up web pages. We used to use Ext but, their licensing switcharoo really soured us on that toolkit. As well Dojo and jQuery do not conflict so if absolutely necessary one can leverage existing jQuery code in a Dojo app. You can email me or post to the thread if you want to know any specifics about how we built it. We have larger corp apps that we have done but the following are some public facing apps that we built, there is also the back end admin systems for these apps but that is not publicly avalible:
http://www.ibm.com/social/northstar/
http://www.ibm.com/social/informationondemand/