I think that they will be popular as a deployment model for applications that use the SharePoint.Client namespace with javascript and Silverlight. I can certainly hide the ribbon with javascript on the client – but I shouldn’t have to. I remain concerned that there is no good answer to #2 with regards to client side code. It would be nice if SharePoint allowed some sort of trusted caller infrastructure that allowed elevation to site owner. This should be possible at least with Silverlight

Getting started with jQuery in SharePoint is surprisingly easy (to me). (I do have serious questions about a “best practices” approach to deploying these things to production, but that’s for another day). I’ve just started playing with this technology and to that end, I created a sandbox environment to use. If you’re looking to get started with jQuery, you may find this approach useful.