I haven't used WCF Data Services for web forms development, yet - but the main project that I work on is next on my list to start building some WCF-DS/OData functionality for.
It's definitely something that's possible, and I think it provides a nice add-on to an existing site/application that you either want to provide some queryable feeds for and/or some additional CRUD functionality. My issue, right now, is that my web forms project does not use the Entity Framework as the underlying domain model - we have a hand-rolled set of entities. So I'll have to do a lot of (somewhat mundane) work implementing IUpdatable for the insert/update/delete functionality. But I'll get the IQueryable side of things up and running quickly in order to provide some quick wins in terms of disseminating information from the application. (Might as well go with the low-hanging fruit first to see if it's worth the effort -- I'm sure it will be worth it, but I'm also going for the quick win!)
I have given some talks around my region on WCF Data Services and OData and have leveraged a lot of jQuery for my examples. Personally, I love it. The JSON format that WCF-DS supports is great and fits in perfectly with my jQuery work.
I've integrated WCF-DS feeds in with some jQuery UI items (modals to display and/or update data, different parts of a feed on different tabs (retrieved asynchronously), etc.) and also am planning on integrating some jqGrid samples I have with my WCF-DS feeds.
If you go with jQuery, I would definitely recommend keeping everything JSON (obviously) and you really shouldn't have any issues.
Let me know if you have other questions about this. I'm surprised there aren't more answers or feedback. I think this is a really nice framework ot integrate into a number of different types of apps (web forms, jQuery, Silverlight, etc.).
Hope this helps! Good luck!!