UkiJS (http://ukijs.org/ http://ukijs.org/) is pretty nice too. I took a serious look at SproutCore and Cappuccino for a web app (not site) that I'm building,

UkiJS (http://ukijs.org/ http://ukijs.org/) is pretty nice too. I took a serious look at SproutCore and Cappuccino for a web app (not site) that I'm building, but jQuery is so damned easy to use, that it was not easy to justify spending a few days learning yet another framework. The thing that made me totally drop any further investigation into SproutCore and Cappuccino (and UkiJS, for that matter) was the JQuery layout plugin (http://layout.jquery-dev.net/ http://layout.jquery-dev.net/). It makes your GUI construction super simple, and then you can cherry pick the jQuery UI elements that work for you.